Re: Scope of committee (can we do *new* things?)

[Andres Loeh]

I think we all agree that in general, we should focus on existing
language extensions that have an implementation, and expect language
extensions to be implemented for them to be seriously considered for
inclusion in the standard.

But I think it would be wrong to turn this into a hard rule. Language
extensions are usually looked at in isolation, whereas the standard is
supposed to be a whole. There may be things that fit in well, are
useful generalizations of extensions we want to adopt, and so on that
are worth discussing. Also, extensions should perhaps be modified or
changed in some cases. If we say in advance that we can only
standardize things that GHC already implements, and only in exactly
this way, then it is a bit too limiting, and this would be throwing
away the chance to clean up a few issues.

The other side of this is that if we really arrive at the conclusion
that something should be different from the current GHC
implementations in any significant way, we should at least try to get
it implemented during, and not just after, the standardization process
so that we can still get practical feedback, and to prevent ending up
with a standard that will never be implemented.

Also (I think I've said this before), we should keep in mind that the
whole process for Haskell 2020 can have more outputs than just the new
standard itself. We can make progress towards standardization of
features in future versions of Haskell even if they don't yet make it.
We can make statements that we would in principle like to see certain
features in the standard, and identify the issues that currently
prevent them from being included.

Cheers,
  Andres

On Thu, May 12, 2016 at 9:46 PM, Iavor Diatchki
 wrote:
> I disagree that we should be standardizing language features that have not
> been implemented.
>
> I think having an implementation is important because:
>1. the act of implementing a feature forces you to work out details that
> you may not have thought of ahead of time.  For example, for a small
> syntactic extension, the implementation would have to work out how to fit it
> in the grammar, and how to present the new feature in, say, error messages.
>2. having an implementation allows users to try out the extension and
> gain some empirical evidence that the extension is actually useful in
> practice (this is hard to quantify, I know, but it is even harder if you
> can't even use the extension at all).
>
> If some feature ends up being particularly useful, it could always be
> standardized in the next iteration of the language, when we've gained some
> experience using it in practice.
>
> -Iavor
>
>
>
> On Wed, May 11, 2016 at 11:17 AM, John Wiegley 
> wrote:
>>
>> > Gershom B  writes:
>>
>> > While such changes should definitely be in scope, I do think that the
>> > proper
>> > mechanism would be to garner enough interest to get a patch into GHC
>> > (whether through discussion on the -prime list or elsewhere) and have an
>> > experimental implementation, even for syntax changes, before such
>> > proposals
>> > are considered ready for acceptance into a standard as such.
>>
>> Just a side note: This is often how the C++ committee proceeds as well: a
>> language proposal with an experimental implementation is given much higher
>> credence than paperware. However, they don't exclude paperware either.
>>
>> So I don't think we need to rely on implementation before considering a
>> feature we all want, but I do agree that seeing a patch in GHC first
>> allows
>> for much testing and experimentation.
>>
>> --
>> John Wiegley  GPG fingerprint = 4710 CF98 AF9B 327B B80F
>> http://newartisans.com  60E1 46C4 BD1A 7AC1 4BA2
>> ___
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>
>
>
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Re: Are there GHC extensions we'd like to incorporate wholesale?

[Andres Loeh]

Hi.

Just to add a few general points. There are different dimensions to
evaluate GHC extensions for inclusion in the standard, and just making
lists does not really reflect that. The two most important ones, I
think, are:

1. Whether we think they're actually a good idea or not.

2. Whether we think they're feasible to specify in a sensible way.

There are variations of these points (extensions that are perhaps
possible to specify, but ugly in their current form; extensions that
have subtle interactions with others; ...)

In general, I am in favour on working on extensions for which we
believe they're good ideas, and try to make progress, even if we
cannot include them yet. So just as an example, if we think GADTs (and
not just GADTSyntax) are in principle a good idea and should be in a
future standard, then perhaps we can try to work out what exactly we
feel would be needed to include them, but is still missing. Then even
in times when no standardization process is active, people can look at
this list of issues and try to work on them. I also think that we
should be careful with straight-forward looking syntax extensions.
Just because an extension is easy to specify should not make it an
automatic accept either. The complexity of the language is already
high.

All this being said, I still have a personal list:

BangPatterns
ConstrainedClassMethods
ConstraintKinds (?)
Derive* (?)
EmptyCase
ExistentialQuantification
ExplicitForAll
ExplicitNamespaces
ExtendedDefaultRules (?)
FlexibleContexts
FlexibleInstances
GADTSyntax
InstanceSigs
KindSignatures
NullaryTypeClasses
Overloaded* (?)
PartialTypeSignatures (?)
RankNTypes
ScopedTypeVariables
StandaloneDeriving (?)
TypeSynonymInstances
TypeOperators (?)

I probably forgot a few. For the ones listed with (?), I am aware of
some problems, but I'd still be very happy to at least have some
discussions about them and make some progress in the direction of
future standardization, as I indicated above.

Cheers,
  Andres

On Tue, May 3, 2016 at 7:32 AM, M Farkas-Dyck  wrote:
> On 02/05/2016, Cale Gibbard  wrote:
>> Are there extensions which ought to stop being extensions?
>
>> It may also be best to leave the answer up to the implementations. It is much
>> easier to argue for something like that once the extension has been on by
>> default in GHC and all other implementations for a while and most everyone
>> seems happy leaving it on.
>
> I think in many cases that would defeat the purpose of extensions.
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Re: Infrastructure & Communication

[Andres Loeh]

Hi.

I'm ok with the general proposals made by Herbert. I'm not a huge fan
of github myself, but it seems like the most pragmatic choice right
now, and I wouldn't know anything else that is clearly better, so I'm
in favour. I'd somewhat prefer to have everything (wiki etc) in one
place then, but I don't have strong opinions on this topic.

Cheers,
  Andres
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Re: Update on Haskell Prime reboot?

[Andres Loeh]

Hi.

I've been talking to Herbert from time to time, and I know he's having
a draft announcement lying around, and is still planning on properly
starting the process soon, and has (this is my opinion, not his) just
been falling into the trap of waiting for a "good moment" which then
never comes.

I'm personally still eager to get the discussions about a new standard started.

While it's true that the old Haskell Prime committee has been doing
good work in creating some sort of catalogue of issues and extensions
at the time, it's still far from proper standardization. And indeed, I
think the bulk of the work that goes into a new standard in my opinon
is to work out all the corner cases and the actual specification of
the extensions. It's less important which ones ultimately go in or
stay out, but actually specfiying them properly is already going to be
a good step forward.

Cheers,
  Andres


On Fri, Apr 22, 2016 at 7:55 PM, José Manuel Calderón Trilla
 wrote:
> Hi Richard,
>
>> As a concrete suggestion, I wonder if we should have two goals:
>>
>> 1. Write down an updated standard for Haskell.
>>
>> 2. Write down pre-standards for several extensions.
>
> I agree with both of these. It may even be useful to use goal 2 as a
> stepping stone to determine what extensions should receive the extra
> attention necessary (if any) to be part of goal 1. Were you thinking
> that these pre-standards would look something like Mark Jones's
> 'Typing Haskell in Haskell' paper? A simplified and clear
> specification in the form of a Haskell program would go a long way in
> clarifying the meaning of certain extensions. To use your example, you
> could imagine an implementation of GADTs that forms the baseline of
> what the GADT extension should mean (implementations should accept at
> least what this one does). That might be too ambitious though.
>
> A lot of the 'obvious' extensions were discussed that last time the
> Haskell Prime committee was active, so a lot of groundwork has been
> laid already. The most important step right now is empowering people
> to move forward with the process.
>
> Herbert Valerio Riedel is the chair of the reboot, and as such gets
> final say on who is a member of the committee and any timeline for
> deciding. That being said, I think the aim should be to have the
> committee membership decided soon and start discussing what the
> priorities should be. I'm partial to suggesting a face to face meeting
> at ICFP, but realize that it is difficult for many to attend to ICFP.
>
> Cheers,
>
> José
>
>
> On Fri, Apr 22, 2016 at 9:33 AM, Richard Eisenberg  wrote:
>> I stand by ready to debate standards and would enjoy moving this process 
>> forward. However, I'm not in a position where I can lead at the moment -- 
>> just too consumed by other tasks right now.
>>
>> As a concrete suggestion, I wonder if we should have two goals:
>>
>> 1. Write down an updated standard for Haskell.
>>
>> 2. Write down pre-standards for several extensions.
>>
>> About (2): I'm very sympathetic to a recent post on Haskell-cafe about 
>> having formal descriptions of language extensions. It is not our purview to 
>> document GHC. However, several extensions are in very common use, but might 
>> not be quite ready for a language standard. Chief among these, in my 
>> opinion, is GADTs. GADTs are problematic from a standardization standpoint 
>> because it's quite hard to specify when a GADT pattern-match type-checks, 
>> without resorting to discussion of unification variables. For this reason, I 
>> would be hesitant about putting GADTs in a standard. On the other hand, it 
>> shouldn't be too hard to specify some sort of minimum implementation that 
>> individual compilers can build on. I'm calling such a description a 
>> "pre-standard".
>>
>> Thoughts?
>>
>> Richard
>>
>> On Apr 21, 2016, at 5:22 PM, José Manuel Calderón Trilla  
>> wrote:
>>
>>> Hello all,
>>>
>>> I'm curious if there is any progress on the reboot of the Haskell
>>> Prime committee. It has been six months since the closing of
>>> nominations and there hasn't been any word that I'm aware of. I've
>>> also spoken to a few others that have self-nominated and they too have
>>> not heard any news.
>>>
>>> Personally, I feel that a new standard is very important for the
>>> future health of the community. Several threads on the mailing list
>>> and posts on the web, such as one on reddit today [1], show a desire
>>> from the community for a major consolidation effort.
>>>
>>> If there is any way that I can help the process along I would be glad
>>> to do so. It would be a shame to allow for the enthusiasm for a new
>>> committee fade away.
>>>
>>> Cheers,
>>>
>>> José
>>>
>>>
>>> [1]: 
>>> https://www.reddit.com/r/haskell/comments/4fsuvu/can_we_have_xhaskell2016_which_turns_on_the_most/
>>> ___
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>>> Haskell-prime@haskell.org
>>> 

[Haskell] CFP: Workshop on Generic Programming 2012

[Andres Loeh]

 related) DGP workshops in Oxford (June
3-4 2004), and a Spring School on DGP in Nottingham (April 24-27
2006, which had a half-day workshop attached).

WGP Steering Committee
--

Patrik Jansson (chair)
Sibylle Schupp
Bruno Oliveira
Marcin Zalewski
Jaako Järvi
Shin-Cheng Mu
Jeremy Gibbons
Magne Haveraaen
Tim Sheard

-- 
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Well-Typed LLP, http://www.well-typed.com

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Re: [Haskell-cafe] SIGPLAN Programming Languages Software Award

[Andres Loeh]

I think the history of generics in Java is

Pizza (http://pizzacompiler.sourceforge.net/) -
GJ (http://lamp.epfl.ch/pizza/gj/) -
Java

I think that if you consider that history, and in particular the Pizza
compiler, then the connection to FP becomes rather obvious.

Cheers,
  Andres

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Re: [Haskell-cafe] cap 3: stopping thread 3 (stackoverflow)

[Andres Loeh]

I don't think a stack overflow event indicates an RTS bug. Stack
overflow events usually result in the RTS trying to adjust the stack
size, and only if that fails, the program is halted.

 (... and why can't I copy/paste the text from threadscope's output window)

As a workaround, you can use the show-ghc-events binary that is
provided by the ghc-events package.

Cheers,
  Andres

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Re: [Haskell-cafe] Cabal: top level dependency base -any

[Andres Loeh]

Hi.

 Could anyone shed light on the meaning of this error message?

 cabal: cannot configure xmonad-0.9.1 It requires base ==3.*
 For the dependency on base ==3.* there are these packages: base-3.0.3.1 and
 base-3.0.3.2. However none of them are available.
 base-3.0.3.1 was excluded because of the top level dependency base -any
 base-3.0.3.2 was excluded because of the top level dependency base -any

It's not a great error message. Yes, xmonad-0.9.1 requires base ==3.*.
So far, so good. Now, base is a special package. It comes with ghc,
and cannot be upgraded. That's why Cabal will rule out all base
versions but the one you already have installed. If you have a recent
ghc, that'll be base-4.

So Cabal is correct to fail in this case: you cannot install this
version of xmonad with this version of ghc. But yes, the error message
could (and hopefully soon will) be improved.

Cheers,
  Andres

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Re: [Haskell-cafe] Cabal: top level dependency base -any

[Andres Loeh]

Hi.

 So would it be correct to infer that the -any restriction will only (and
 always) come into play with special packages such as base?

No. Unfortunately, -any really means any version is allowed, so
that's why the error message is really misleading.

 Are there any other special packages besides base?

W.r.t. Cabal's dependency resolution? No.

Cheers,
  Andres

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Re: [Haskell-cafe] Data constructor synonyms

[Andres Loeh]

  Remember that constructors are functions, except that you can't
  pattern match against them.

 ..

  The downside is that you can't pattern-match against these functions.

 The thing is that I need pattern matching, just functions won't do.

It's only a preprocessor, but Conor's she allows pattern synonyms:

http://personal.cis.strath.ac.uk/~conor/pub/she

 Anyway, a new question arose.  If I have already declared a type, can I add 
 new constructors to it from other modules?

Again, not within Haskell itself. she also has a feature that allows
something like this. There are various other techniques or proposals.
For example:

http://www.cs.ru.nl/~wouters/Publications/DataTypesALaCarte.pdf
http://people.cs.uu.nl/andres/OpenDatatypes.html

Cheers,
  Andres

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Re: [Haskell-cafe] lhs2tex and line numbers

[Andres Loeh]

Hi.

 How could I convince lhs2tex to add in poly mode line numbers before
 each code line in code block?

A long time ago, I've written some experimental code that achieves
line numbering in lhs2tex. I've committed the files to the github
repository, so you can have a look at the .fmt file and the demo
document in

https://github.com/kosmikus/lhs2tex/tree/master/ExtLibrary/lineno

HTH,
  Andres

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Re: [Haskell-cafe] lhs2tex build failure

[Andres Loeh]

The latest version on GitHub should fix the problem. I'll make a new
release soon.

https://github.com/kosmikus/lhs2tex

Cheers,
  Andres

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Re: Alternative (per-project) package database

[Andres Loeh]

Hi Dimitry.

Depending on what exactly you're after, you may also be interested in
Nix and/or NixOS:

  http://nixos.org/nix/
  http://nixos.org/

The Nix package manager builds any package in completely isolated
environments and makes sure all dependencies are properly specified.
It is easy to build and install one package in many configurations.
We have an infrastructure for building Cabal packages easily and
quite a number of packages from HackageDB in Nixpkgs (though not as
many as Arch). Nix can be used as a secondary package manager on
other Unix-like systems.

Cheers,
  Andres

-- 

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[Haskell] Final call for participation: Summer school Applied Functional Programming, Aug 16-27, Utrecht NL, Application deadline: May 1

[Andres Loeh]

[Feel free to advertise the school to others who might be interested.]

~~
Utrecht Summer School in Computer Science: Applied Functional Programming

August 16-27, 2010
Utrecht, The Netherlands
~~

The summer school is intended as a first or an advanced course on
Haskell, consisting of lectures and projects to be solved by the
participants, working in teams. We mainly target bachelor and master
students, but others who are interested are also welcome to apply.

The deadline for applications is *** Saturday, May 1, 2010 ***.


More information:

http://www.cs.uu.nl/wiki/USCS2010

If you have any questions, feel free to contact me.

Cheers,
  Andres


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Re: [Haskell-cafe] Re: Hackage accounts and real names

[Andres Loeh]

  Let me summarise the main arguments against the restriction:
 
  1. It stops people from contributing [..]
  2. Inconsistency [..]
  3. Privacy issues [..]
 
 4. It inteferes with people's freedom - who has the right to dictate what 
 name a person (or, for that matter, a group of people) should be known
 as?
 
 5. It encourages dishonesty: if you want to contribute but not reveal
 your real name, you have the option to lie about it, and can be fairly
 confident your lie will never be called.
 
 +1 for allowing nicks.

Another +1 from me.

I must admit that I had never really thought about this restriction, but
the arguments against the restriction clearly convince me. I have heard
no valid arguments in favour of the restriction. I can see that there are
advantages to requiring real names, but that only makes sense if it is
enforced (and I certainly don't advocate that). The way it is now, where
some people who just silently use pseudonyms get accounts, and others,
who are not willing to lie, are rejected, is very bad.

If people are really worried about trust, then a comment/reviewing
system for Hackage is a better solution.

Cheers,
  Andres

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[Haskell] Summer School Applied Functional Programming, 16-27 Aug 2010, Utrecht, NL

[Andres Loeh]

[Feel free to advertise the school to others who might be interested.]

Call for participation:

~~
Utrecht Summer School in Computer Science: Applied Functional Programming

August 16-27, 2010
Utrecht, The Netherlands
~~

We offer a summer school that may be interesting to Haskellers on this
mailing list. We mainly target bachelor and master students, but others
who are interested are also welcome to apply.

The deadline for applications is May 1, 2010.


More information:

http://www.cs.uu.nl/wiki/USCS2010

If you have any questions, feel free to contact me.

Cheers,
  Andres


-- 

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Re: [Haskell-cafe] Haskell course, training

[Andres Loeh]

Hi Günther,

 all going well this year I'll be able to invest some money on becoming a 
 better Haskeller.

 I think I've reached the point where I need some tutoring, so provided I've 
 got money for travel and course fees, and time, where do I get it? I'm not 
 a student so some courses aren't available to me.

please consider the summer school in Applied Functional Programming
that we at Utrecht University are going to offer this year for the
second time:

http://www.utrechtsummerschool.nl/index.php?type=coursescode=H9

While the school is mainly aimed at students (bachelor- and
master-level), we have no formal requirement that participants must be
students, and we will certainly consider other applications.

Cheers,
  Andres

-- 

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[Haskell-cafe] Re: lhs2TeX \eval{} problem

[Andres Loeh]

Hi.

 I'm having a problem with lhs2Tex and \eval{}. It doesn't work.
 
 I have the following in a file test.lhs:
 
 
 %include polycode.fmt
 
 One
 %option ghci
 Two
 \eval{4}
 Three
 
 
 When I try to run this file through lhs2Tex, it crashes:
 
  lhs2Tex test.lhs
 ... polycode junk removed ...
 
 One
 %option ghci
 Two
 lhs2TeX: fd:7: hGetLine: end of file
 
 
 
 Has someone encountered this problem before, or knows how to solve this?

Two issues:

First, it's

%options ghci

and not

%option ghci

Second, the \eval is executed in the context of the current file,
i.e., the source must be a valid literate Haskell file. An empty
literate file causes the literate preprocessor to fail. This
works for me:


%include polycode.fmt

One
%options ghci
Two
\eval{4}
Three

 x = 0


HTH,
  Andres

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Re: [Haskell-cafe] Re: lhs2TeX \eval{} problem

[Andres Loeh]

 Oh, well that teaches me not to type myself... Copy-and-paste is way better!
 
 Now lhs2TeX no longer crashes, unfortunately it still doesn't work correctly.
 
 It now simply hangs after printing the line Two.
 It doesn't crash, or eat memory or cpu. It just sits there, doing
 nothing, until I kill the process.

Are you sure you added the extra line at the end? Try to call ghci
on the source file. If it manages to load it without errors, then
lhs2TeX should succeed as well.

Cheers,
  Andres

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[Haskell-cafe] ANN: lhs2tex-1.15 (was: lhs2tex, Haskell Platform and cygwin)

[Andres Loeh]

 Also, it would be nice if there were an lhs2tex version which worked 
 out-of-the-box with base=4, since hacking the Makefile for that seems, er, 
 sub-optimal?

I've just uploaded 1.15 which should work better on Windows. Sorry, I
should have released a new version a long time ago. Please let me know
if this works.

Cheers,
  Andres

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Re: [Haskell-cafe] lhs2tex + pretty print

[Andres Loeh]

The attached document works for me.

HTH,
  Andres

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\documentclass{article}

%include polycode.fmt
%options ghci

\begin{document}

\section{Test}

 test = putStrLn \\section{Result}\n\nIt works!

\perform{test}

\end{document}
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Re: [Haskell-cafe] Functors and the Visitor Pattern

[Andres Loeh]

 Although, now I'm second guessing myself, because I can't figure out how we
 could create some design pattern that simulates an applicative functor. I'm
 pretty sure the Visitor pattern doesn't take you this far (but I am willing
 to be corrected). So, is there a way to create applicative functors in
 non-functional languages? What would that pattern look like?

Perhaps this paper can answer your question:

Jeremy Gibbons, Bruno C.d.S. Oliveira
The essence of the Iterator pattern
http://web.comlab.ox.ac.uk/oucl/work/jeremy.gibbons/publications/iterator.pdf

HTH,
  Andres

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[Haskell] Call for Participation: Utrecht Summer School on Applied Functional Programming

[Andres Loeh]

Call for participation:

~~~
Utrecht Summer School in Computer Science: Applied Functional Programming

August 17-28, 2009
Utrecht, The Netherlands
~~~

We are offering a summer school that may be interesting to Haskell beginners on
this list. We mainly target bachelor and master students, but others interested
are also welcome to apply.

Note that the deadline for applications is very soon; May 1, 2009.

More information:
http://www.utrechtsummerschool.nl/index.php?type=coursescode=H9

Cheers,
  Andres

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Re: [Haskell-cafe] The votes are in!

[Andres Loeh]

 The results of the Haskell logo competition are in!

 You can view them at 
 http://www.cs.cornell.edu/w8/~andru/cgi-perl/civs/results.pl?num_winners=1id=E_d21b0256a4fd5ed7algorithm=beatpath

 Congratulations Jeff Wheeler!

 Is there also a measure of how strong the winner wins over the losers?

Scroll to the bottom of the results page linked above and click on the
button, and you'll get a matrix comparing each logo to each other logo.
You still have to interpret the results yourself, though.

Cheers,
  Andres

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Re: [Haskell-cafe] Hac5 projects page

[Andres Loeh]

 on http://www.haskell.org/haskellwiki/Hac5/Projects, you can list a project 
 under “Project descriptions” and under “Experiences”. What’s the difference?

Project descriptions are supposed to be projects you're currently
working on or want to work on during the Hackathon.

Experiences are not necessarily projects (and feel free to update the
description on the page to reflect that), but general Haskell-related
things you are familiar with. So, if for example I am looking for
someone with a lot of experience in writing library bindings using the
FFI, I could look in that list if anyone attending might be able to help
me ...

HTH,
  Andres

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[Haskell] ANNOUNCE: multirec-0.2

[Andres Loeh]

multirec-0.2: Generic programming with systems of recursive datatypes
=

Many generic programs require information about the recursive positions
of a datatype. Examples include the generic fold, generic rewriting or
the Zipper data structure. Several generic programming systems allow to
write such functions by viewing datatypes as fixed points of a pattern
functor. Traditionally, this view has been limited to so-called regular
datatypes such as lists and binary trees. In particular, systems of
mutually recursive datatypes have been excluded.

With the multirec library, we provide a mechanism to talk about fixed
points of systems of datatypes that may be mutually recursive. On top
of this representations, generic functions such as the fold or the Zipper
can then be defined.

Changelog (changes w.r.t. multirec-0.1)
---

* Constructor information and generic show (Generics.MultiRec.Show).

* Variants of fold (Generics.MultiRec.FoldAlg) that make the definition of
  algebras significantly more convenient.

* Template Haskell code to generate the boilerplate required to
  instantiate this library to a system of datatypes.

Requirements


* GHC 6.8.3 or later
* Cabal 1.2.1 or later

Download


With cabal-install:

  cabal install multirec

Get the package:

  http://hackage.haskell.org/cgi-bin/hackage-scripts/package/multirec

Get the source:

  svn checkout https://svn.cs.uu.nl:12443/repos/dgp-haskell/multirec/trunk

Bugs  Support
--

Report issues, request features, or just discuss the library with the
authors, maintainers, and other interested persons at:

   http://www.haskell.org/mailman/listinfo/generics

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[Haskell] ANNOUNCE: zipper-0.1

[Andres Loeh]

zipper-0.1: Generic zipper for systems of recursive datatypes
=

The zipper is a data structure that allows typed navigation on a value.
It maintains a subterm as a current point of focus. The rest of the value
is the context. Focus and context are automatically updated when navigating
up, down, left or right in the value. The term that is in focus can also
be modified.

This library offers a generic zipper for systems of datatypes. In particular,
it is possible to move the focus between subterms of different types, in an
entirely type-safe way. This library is built on top of the multirec library,
so all that is required to get a zipper for a datatype system is to instantiate
the multirec library for that system.

Requirements


* GHC 6.8.3 or later
* Cabal 1.2.1 or later

Download


With cabal-install:

  cabal install zipper

Get the package:

  http://hackage.haskell.org/cgi-bin/hackage-scripts/package/zipper

Get the source:

  svn checkout https://svn.cs.uu.nl:12443/repos/dgp-haskell/zipper/trunk

Bugs  Support
--

Report issues, request features, or just discuss the library with the
authors, maintainers, and other interested persons at:

   http://www.haskell.org/mailman/listinfo/generics

-- 

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[Haskell] type family vs. polymorphism

[Andres Loeh]

Hi.

Here's a strange interaction of type families and higher-rank
polymorphism (tested with both ghc-6.8.3 and ghc-6.10.1):

{-# LANGUAGE TypeFamilies, EmptyDataDecls, RankNTypes #-}

data X (a :: *)
type family Y (a :: *)

-- This works (datatype).
i1 :: (forall a. X a) - X Bool
i1 x = x 

-- This works too (type family and extra arg).
i2 :: (forall a. a - Y a) - Y Bool
i2 x = x True

-- This doesn't work (type family).
-- i3 :: (forall a. Y a) - Y Bool
-- i3 x = x

I would expect i3 to be ok as well. Note that this is a
simplified example and not really useful in its simplified
form.

Cheers,
  Andres

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Re: [Haskell-cafe] Type wildcards

[Andres Loeh]

 Type wildcards that allow partially specifying types, e.g:
 
 f :: _ - String
 f x = show x
 
 This will instruct the type-inferrer to fill out the wild-card part only
 (e.g: Show a = a).

Also see

http://hackage.haskell.org/trac/haskell-prime/wiki/PartialTypeAnnotations

Cheers,
  Andres

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Re: [Haskell-cafe] Associated data types

[Andres Loeh]

Hi.

 Date: Wed, 10 Dec 2008 13:36:11 +
 From: Lennart Augustsson [EMAIL PROTECTED]
 Subject: Re: [Haskell-cafe] Associated data types
 
 For an associated data type D, we know that the type function D is
 injective, i.e., for different indicies given to D we'll get different
 data types.  This makes much more powerful reasoning possible in the
 type checker.  If associated data types are removed there has to be
 some new mechanism to declare an associated type as injective, or the
 type system will lose power.
 
   -- Lennart
 
 2008/12/10 Eyal Lotem [EMAIL PROTECTED]:
  If we have associated type synonyms, is there still reason to have
  associated data types?

[...]

Another, somewhat related, issue is that associated type synonyms cannot
currently be partially applied, whereas associated data types can.

Cheers,
  Andres

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[Haskell] ANNOUNCE: multirec-0.1

[Andres Loeh]

multirec: Generic programming with systems of recursive datatypes
=

Many generic programs require information about the recursive positions
of a datatype. Examples include the generic fold, generic rewriting or
the Zipper data structure. Several generic programming systems allow to
write such functions by viewing datatypes as fixed points of a pattern
functor. Traditionally, this view has been limited to so-called regular
datatypes such as lists and binary trees. In particular, systems of
mutually recursive datatypes have been excluded.

With the multirec library, we provide a mechanism to talk about fixed
points of systems of datatypes that may be mutually recursive. On top
of this representations, generic functions such as the fold or the Zipper
can then be defined.

We expect that the library will be especially interesting for compiler
writers, because ASTs are typically systems of mutually recursive datatypes,
and with multirec it becomes easy to write generic functions on ASTs.

The library is based on ideas described in the paper:

  Alexey Rodriguez, Stefan Holdermans, Andres Löh, Johan Jeuring
  Generic programming with fixed points for mutually recursive datatypes
  Technical Report, Universiteit Utrecht
  http://www.cs.uu.nl/research/techreps/repo/CS-2008/2008-019.pdf

Features


* Generalizes the fixed point view from single, regular datatypes to systems
  of recursive datatypes.

* Includes detailed examples: generic fold and generic compos, the latter
  in the style of

Björn Bringert, Arne Ranta
A pattern for almost compositional functions
ICFP 2006
  
  The Zipper and generic rewriting for systems of datatypes 
  will be released soon as separate libraries that build on multirec.

* The generic compos functions do not require the user to modify
  their existing systems of datatypes.

* In its current form, this library does not support nested datatypes.

Requirements


* GHC 6.8.3 or later
* Cabal 1.2.1 or later

Download


With cabal-install:

  cabal install multirec

Get the package:

  http://hackage.haskell.org/cgi-bin/hackage-scripts/package/multirec

Get the source:

  svn checkout https://svn.cs.uu.nl:12443/repos/dgp-haskell/multirec/trunk

Bugs  Support
--

Report issues, request features, or just discuss the library with the
authors, maintainers, and other interested persons at:

   http://www.haskell.org/mailman/listinfo/generics


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[Haskell] ANNOUNCE: lhs2tex-1.14

[Andres Loeh]

 lhs2TeX version 1.14
 

We are pleased to announce a new release of lhs2TeX, 
a preprocessor to generate LaTeX code from literate Haskell
sources.

lhs2TeX includes the following features:

* Highly customized output.

* Liberal parser -- no restriction to Haskell 98.

* Generate multiple versions of a program or document from 
  a single source.

* Active documents: call Haskell to generate parts of the 
  document (useful for papers on Haskell).

* A manual explaining all the important aspects of lhs2TeX.

Changes (w.r.t. lhs2TeX 1.13)
-

* Compatible with cabal-1.6; traditional configure/make
  installation should still work.

* Unicode support.

* Support for Agda's lexing rules (via --agda flag).

* Minor bugfixes.

Requirements and Download
-

A source distribution is available from

  http://people.cs.uu.nl/andres/lhs2tex/

and, of course, via Hackage:

  http://hackage.haskell.org/cgi-bin/hackage-scripts/package/lhs2tex

Should work on all major platforms, but has mainly been
tested on Linux. Binaries will be made available on request.

You need a recent version of GHC (6.8.{2,3} are tested, older versions
might work) to build lhs2TeX, and, of course, you need a TeX
distribution to make use of lhs2TeX's output. The program includes
a configuration that is suitable for use with LaTeX. In theory, 
there should be no problem to generate code for other TeX 
flavors, such as plainTeX or ConTeXt.


  Happy lhs2TeXing,
  Andres Loeh and Ralf Hinze

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[Haskell] Change of Editor HCAR (Haskell Communities and Activities Report)

[Andres Loeh]

Dear Haskellers.

The Haskell Communities and Activities Report (HCAR) for short is a
collection of status reports and news items from projects, groups,
companies, and individuals that appears twice per year.

As of now, the latest issue is from December 2007 and available from
http://haskell.org/communities. I have been the editor of the report for
the last six editions, and have recently been looking for a successor.
It is my pleasure to announce that

  Janis Voigtlaender, Technical University of Dresden

has declared himself willing to perform this task, starting with the
next issue, which will have a deadline very soon, probably in the
beginning of May. I want to use this opportunity to thank Janis for
accepting the responsibility and thereby helping to keep this valuable
information source alive. I also want to thank all the contributors to
the HCAR for supporting it during the past years and ask you to support
Janis in his job by submitting many new entries in time for the
deadline, as you usually did when I was the editor.

Cheers,
  Andres

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[Haskell] Advert: Software Technology Master at Utrecht University

[Andres Loeh]

Haskell enthusiasts looking for an interesting and challenging Master program
should consider the Software Technology program at Utrecht University.

The Master Program Software Technology studies techniques that are employed 
in the production of software. We start from sound theoretical foundations, 
with a strong focus on real applicability. The program includes courses on 
programming methodology, programming formalisms (languages), programming 
tools, software architectures, component based programming, specification 
formalisms and verification techniques (correctness proofs, theorem 
proving).

Almost all of our courses use Haskell as the main implementation
language, and we have many courses that are specifically targeted
at functional programmers such as Implementation of Programming
Languages, Advanced Functional Programming and Generic Programming.
Furthermore, we have regular seminars on topics such as Type Systems, 
Dependently-Typed Programming, Program Analysis or Advanced
Compiler Construction.

The Master Program is internationally oriented: the program is open to 
foreign students, and courses are taught in English. Students have the 
opportunity to follow courses and do projects at foreign universities and 
institutes. The program caters for students with a desire to obtain a Ph.D. 
position or a research position in a company, and for students who are 
interested in jobs as software designer in industry. The program results in 
a degree Master of Science in Computer Science. The program is offered by 
the Center for Software Technology of the Institute of Information and 
Computing Sciences at Utrecht University.

For more information, see

  http://www.cs.uu.nl/wiki/Master
  http://www.cs.uu.nl/wiki/Master/MasterCourses


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[Haskell] ANNOUNCE: lhs2tex-1.13

[Andres Loeh]

 lhs2TeX version 1.13
 

We are pleased to announce a new release of lhs2TeX, 
a preprocessor to generate LaTeX code from literate Haskell
sources.

lhs2TeX includes the following features:

* Highly customized output.

* Liberal parser -- no restriction to Haskell 98.

* Generate multiple versions of a program or document from 
  a single source.

* Active documents: call Haskell to generate parts of the 
  document (useful for papers on Haskell).

* A manual explaining all the important aspects of lhs2TeX.

Changes (w.r.t. lhs2TeX 1.12)
-

* Compatible with ghc-6.8.{1,2}.

* Compatible with cabal-1.2; traditional configure/make
  installation should still work.

* Uses filepath.

* LINE pragmas can be disabled with --no-pragmas.

* Fixed comment lexing bugs (-- was considered a Haskell comment,
  \% was considered a TeX comment)

* Added a %subst directive for backquoted operators.

Requirements and Download
-

A source distribution is available from

  http://www.cs.uu.nl/~andres/lhs2tex/

Should work on all major platforms, but has mainly been
tested on Linux. Binaries will be made available on request.

You need a recent version of GHC (6.8.2 is tested, older versions
might work) to build lhs2TeX, and, of course, you need a TeX
distribution to make use of lhs2TeX's output. The program includes
a configuration that is suitable for use with LaTeX. In theory, 
there should be no problem to generate code for other TeX 
flavors, such as plainTeX or ConTeXt.


  Happy lhs2TeXing,
  Andres Loeh and Ralf Hinze

  [EMAIL PROTECTED]

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[Haskell] 2nd ANNOUNCE: HCAR 12/2007

[Andres Loeh]

Hi everyone.

[For everyone who missed the first announcement because they were
already in the holidays ...]

The December 2007 edition of the Haskell Communities and Activities
Report is out and available for download from

  http://haskell.org/communities

Cheers,
  Andres 

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[Haskell] ANNOUNCE: Haskell Communities Activities Report (13th ed., December 2007)

[Andres Loeh]

On behalf of the many, many contributors, I am pleased to announce
that the

  Haskell Communities and Activities Report
(13th edition, December 2007)

 http://www.haskell.org/communities/

is now available from the Haskell Communities home page in PDF and
HTML formats.

Many thanks go to all the people that contributed to this report,
both directly, by sending in descriptions, and indirectly, by doing
all the interesting things that are reported. I hope you will find
it as interesting a read as we did.

If you haven't encountered the Haskell Communities and Activities 
Reports before, you may like to know that the first of these reports
was published in November 2001. Their goal is to improve the 
communication between the increasingly diverse groups, projects and
individuals working on, with, or inspired by Haskell. The idea behind
these reports is simple:

Every six months, a call goes out to all of you enjoying Haskell to
contribute brief summaries of your own area of work. Many of you 
respond (eagerly, unprompted, and well in time for the actual 
deadline ;) ) to the call. The editor collects all the contributions 
into a single report and feeds that back to the community.

When we try for the next update, six months from now, you might want 
to report on your own work, project, research area or group as well.
So, please put the following into your diaries now:


End of April 2008:
target deadline for contributions to the
May 2008 edition of the HCA Report


Unfortunately, many Haskellers working on interesting projects are so
busy with their work that they seem to have lost the time to follow
the Haskell related mailing lists and newsgroups, and have trouble even
finding time to report on their work. If you are a member, user or 
friend of a project so burdened, please find someone willing to make 
time to report and ask them to `register' with the editor for a simple 
e-mail reminder in the middle of April (you could point me to them as 
well, and we can then politely ask if they want to contribute, but it 
might work better if you do the initial asking). Of course, they will
still have to find the ten to fifteen minutes to draw up their report,
but maybe we can increase our coverage of all that is going on in the
community.

Feel free to circulate this announcement further in order to
reach people who might otherwise not see it. Enjoy!

Andres Loeh 
hcar at haskell.org

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[Haskell] REMINDER: HCA Report (December 2007 edition)

[Andres Loeh]

Dear Haskellers,

the deadline for the December 2007 edition of the Haskell Communities
and Activities Report is only a few days away. If you haven't already,
please write an entry for your new project, or update your old entry.

Until now, I have about 30 reactions. This is okay compared to the
development of previous editions, but not enough given the number of
announcements on this list during the past months. Also, many regular
contributors haven't yet submitted their entries. Please do!

The deadline is Friday,

   7 December 2007.

If you absolutely cannot make it by Friday, I may be able to give a
few days extension on an individual basis. Please contact me if you
have any questions.

Please mail your entries to hcar at haskell dot org, in plain text
or pseudo-(La)TeX format. More information can be found in the
original Call for Contributions at

  http://www.haskell.org/pipermail/haskell/2007-November/019988.html

I look forward to receiving your contributions.

Thanks a lot,

  Andres (current editor)
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[Haskell] Call for Contributions - Haskell Communities and Activities Report, December 2007 edition

[Andres Loeh]

Dear Haskellers,

so much has happened in the Haskell world in the past months.
Therefore, although later than usual, I would very much like
to collect contributions for the 13th edition of the

  
  Haskell Communities  Activities Report  
http://www.haskell.org/communities/

   Submission deadline: 7 December 2007

  (please send your contributions to hcar at haskell.org, in 
 plain text or LaTeX format)
  

This is the short story:

* If you are working on any project that is in some way related
  to Haskell, please write a short entry and submit it to the me. Even if
  the project is very small or unfinished or you think it is not important
  enough -- please reconsider and submit an entry anyway!

* If you are interested any project related to Haskell that has not 
  previously been mentioned in the HCA Report, please tell me, so that I
  can contact the project leaders and ask them to submit an entry.

* Feel free to pass on this call for contributions to others that
  might be interested.

More detailed information:

The Haskell Communities  Activities Report is a bi-annual overview of
the state of Haskell as well as Haskell-related projects over the
last, and possibly the upcoming 6 months. If you have only recently
been exposed to Haskell, it might be a good idea to browse the 
May 2007 edition -- you will find interesting topics described as well
as several starting points and links that may provide answers to many
questions.

Contributions will be collected until the submission deadline. They
will then be compiled into a coherent report that is published online
as soon as it is ready. As always, this is a great opportunity to
update your webpages, make new releases, announce or even start new
projects, or to talk about developments you want every Haskeller to
know about!

As the purpose of the report is to collect recent or current
activities, I encourage you to update all existing summaries and
reports. I will probably drop any topics that have not had any
activity for the past year, i.e., since November 2006, but I would
very much prefer you to present an updated description of the
topic. Of course, new entries are more than welcome.  Reports should
generally be kept brief and informative, ranging from a few sentences
to a few hundred words, to keep the whole report reasonably sized.

Looking forward to your contributions,

Andres (current editor)


FAQ:

Q: Which topics are relevant?

A: *All* topics which are related to Haskell in some way are relevant.  We
usually had reports from users of Haskell (private, academic, or
commercial), from authors or contributors to projects related to Haskell,
from people working on the Haskell language, libraries, on language
extensions or variants. We also like reports over distributions of Haskell
software, Haskell infrastructure, books and tutorials on Haskell. Reports
on past and upcoming events related to Haskell are also relevant. Finally,
there might be new topics I don't even think about. As a rule of thumb: if
in doubt, then it probably is relevant and has a place in the HCAR. You can
also ask the editor.

Q: Is unfinished work relevant? Are ideas for projects relevant?

A: Yes! You can use the HCAR to talk about projects you are currently
working on. You can use it to look for other developers that might help
you. You can use it to write ``wishlist'' items for libraries and language
features you would like to see implemented.

Q: How much should I write?

A: There's no formal limit. But generally, entries should be short and
to the point. A general introduction is helpful. Apart from that, you
should focus on recent or upcoming developments. There also is no minimum
length of an entry! The reports aims at being as complete as possible, so
please consider writing an entry, even if it's only a few lines long.

Q: If I don't update my entry, but want to keep it in the report, what
should I do?

A: Tell me that there are no changes. I will reuse the old entry in this
case, but I might drop it if it's older than a year, to give more room and
more attention to projects that change a lot. Don't resent complete entries
if you haven't changed them.

Q: What format should I write in?

A: The best format is a LaTeX source file, adhering to the template
that's available at:

  http://haskell.org/communities/11-2007/template.tex

There's also a LaTeX style file at

  http://haskell.org/communities/11-2007/hcar.sty

that you can use to preview your entry. If you don't know LaTeX, then use
plain text. If you modify an old entry, I will send you your old entry as a
template within the next days.Please modify that template, rather than
using your own version of the old entry about a template. Don't worry about
writing correct LaTeX, I will be able to handle your file. 

[Haskell] ANNOUNCE: Haskell Communities Activities Report (12th ed., May 2007)

[Andres Loeh]

On behalf of the many, many contributors, I am pleased to announce
that the

  Haskell Communities and Activities Report
   (12th edition, May 2007)

 http://www.haskell.org/communities/

is now available from the Haskell Communities home page in several
PDF and HTML formats.

Many thanks go to all the people that contributed to this report,
both directly, by sending in descriptions, and indirectly, by doing
all the interesting things that are reported. I hope you will find
it as interesting a read as we did.

If you haven't encountered the Haskell Communities and Activities 
Reports before, you may like to know that the first of these reports
was published in November 2001. Their goal is to improve the 
communication between the increasingly diverse groups, projects and
individuals working on, with, or inspired by Haskell. The idea behind
these reports is simple:

Every six months, a call goes out to all of you enjoying Haskell to
contribute brief summaries of your own area of work. Many of you 
respond (eagerly, unprompted, and well in time for the actual 
deadline ;) ) to the call. The editor collects all the contributions 
into a single report and feeds that back to the community.

When we try for the next update, six months from now, you might want 
to report on your own work, project, research area or group as well.
So, please put the following into your diaries now:


  End of October 2007:
target deadline for contributions to the
November 2007 edition of the HCA Report


Unfortunately, many Haskellers working on interesting projects are so
busy with their work that they seem to have lost the time to follow
the Haskell related mailing lists and newsgroups, and have trouble even
finding time to report on their work. If you are a member, user or 
friend of a project so burdened, please find someone willing to make 
time to report and ask them to `register' with the editor for a simple 
e-mail reminder in the middle of April (you could point me to them as 
well, and we can then politely ask if they want to contribute, but it 
might work better if you do the initial asking). Of course, they will
still have to find the ten to fifteen minutes to draw up their report,
but maybe we can increase our coverage of all that is going on in the
community.

Feel free to circulate this announcement further in order to
reach people who might otherwise not see it. Enjoy!

Andres Loeh 
hcar at haskell.org

-- 
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[Haskell] REMINDER: HCA Report (May 2007 edition)

[Andres Loeh]

Dear Haskellers,

the deadline for the May 2007 edition of the Haskell Communities
and Activities Report is only a few days away -- but this is still
enough time to make sure that the report contains a section on *your*
project, on the interesting stuff that you've been doing; using or
affecting Haskell in some way.

Many projects that have been included in former reports have not yet
updated their entries. Please have a look at the November 2006 edition
for reference.

* Has your project been listed in previous Reports, but is not yet
  updated? Please write a short update!

* Are you no longer working on a project that was included in the
  Report? Write up what you are working on instead, and tell me if
  someone else has picked up the project.

* Is some project you have heard about not included in any previous
  Report? Please let me know ...

There is still time to write a completely new entry, on a new
compiler, tool, library, company, user group, idea, ... -- as long as
there is a connection to the Haskell language, there is a place for it
in the Report!

The general deadline is Wednesday,

  02 May 2007,

but I can extend it by a few days on an individual basis. Just please
contact me before the deadline so that I know you are writing.

Please mail your entries to hcar at haskell dot org, in plain text
or pseudo-(La)TeX format. More information can be found in the
original Call for Contributions at

  http://www.haskell.org/pipermail/haskell/2007-April/019340.html

I look forward to receiving your contributions.

Thanks a lot,

  Andres (current editor)

-- 
Haskell Communities and Activities Report (http://haskell.org/communities)
05/2007 edition submission deadline: 02 May 2007 [EMAIL PROTECTED]
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[Haskell] Call for Contributions - HCA Report (May 2007 edition)

[Andres Loeh]

Dear Haskellers,

it is nearly time for the twelfth edition of the

  
  Haskell Communities  Activities Report  
http://www.haskell.org/communities/

 Submission deadline:  2 May 2007

  (please send your contributions to hcar at haskell.org, in 
plain ASCII or LaTeX format)
  

This is the short story:

* If you are working on any project that is in some way related
  to Haskell, write a short entry and submit it to the me. Even
  if the project is very small or unfinished or you think it is 
  not important enough -- please reconsider and submit an entry
  anyway!

* If you are interested any project related to Haskell that has not 
  previously been mentioned in the HCA Report, please tell me, so 
  that I can contact the project leaders and ask them to submit
  an entry.

* Feel free to pass on this call for contributions to others that
  might be interested.

More detailed information:

The Haskell Communities  Activities Report is a bi-annual overview of
the state of Haskell as well as Haskell-related projects over the
last, and possibly the upcoming 6 months. If you have only recently
been exposed to Haskell, it might be a good idea to browse the 
November 2006 edition -- you will find interesting topics described as well
as several starting points and links that may provide answers to many
questions.

Contributions will be collected until the beginning of May. They
will be compiled into a coherent report which will appear sometime
near the end of May. As always, this is a great opportunity to
update your webpages, make new releases, announce of even start new
projects, or to point at some developments you want every Haskeller to
see!

As the purpose of the report is to collect recent or current
activities, I encourage you to update all existing summaries and
reports. I will probably drop any topics that have not had any
activity for the past year, i.e., since June 2006, but I would
very much prefer you to present an updated description of the
topic. Of course, new entries are more than welcome.  Reports should
generally be kept brief and informative, ranging from a few sentences
to a few hundred words, to keep the whole report reasonably sized.

Looking forward to your contributions,

Andres (current editor)

--- topics

New suggestions for current hot topics, activities, projects, etc.
are welcome - especially with names and addresses of potential
contacts, but here is a non-exclusive list of likely topics
(see also http://www.haskell.org/communities/topics.html ):

General Haskell developments
  Haskell implementations
  Haskell extensions
  Standardization (Haskell', ...)
  Documentation
  Libraries
  Papers and Books

Feedback
  Summaries of discussions in specialist mailing lists
  Conference reports
  Community activities
  Other Haskell information channels (TMR, Sequence, HWN, ...)

Announcements
  Upcoming Haskell events
  Everything that's new or has had new releases

Ongoing projects
  Reports on what's happening behind the scenes
  Confirmations that projects are still maintained
  Calls for contributions and contributors

Tutorials

Tools and Applications
  Released and unreleased Haskell applications
  Tools useful for Haskell programmers 
  Experiences with using Haskell for a project
  Commercial uses of Haskell

Even if your topic is not listed in this list, there's a good chance
it has a place in the Report. Please get in touch with me.

If you want to see an entry that hasn't been there in the past, but
you are not the maintainer of the project, then please encourage the
maintainers to write an entry/update, or ask permission to write the
entry yourself.

-- what should I write?

That depends on your topic, but as a general rule, it shouldn't take
you long. A simple sentence or two about your use of Haskell could
go into the Individual Haskellers section. If you're a company, 
or if you're working on a project using Haskell as the implementation
language, a paragraph on that could go into the Applications section.

A typical summary report about a tool/library/project/application/...
would be between 1 and 3 paragraphs of ASCII text (what's it about? 
major topics and results since the last report?  current hot topics?
major goals for the next six months?) plus pointers to material for
further reading (typically to a home page, or to mailing list  
archives, specifications and drafts, implementations, meetings,
minutes, ...).

Browsing through previous editions should give you a good idea of
the variety of possibilities, ranging from very brief to extensive. 

For those who prefer templates to fill in, the report is edited in  
LaTeX, and an entry template might look something like this:

Re: [Haskell-cafe] Function Composition

[Andres Loeh]

 Can anyone explain why Shape.Polygon would have a different type to
 (Shape).Polygon, I thought the brackets would be redundant. Here is
 the output from a Hugs session
 
 Animation :v
 -- Hugs Version 20050113
 Animation :t Shape
 Shape :: Shape - Region
 Animation :t Polygon
 Polygon :: [Vertex] - Shape
 Animation :t (Shape.Polygon)
 Polygon :: [Vertex] - Shape
 Animation :t ((Shape).Polygon)
 Shape . Polygon :: [Vertex] - Region
 Animation :t Shape.(Polygon)
 Shape . Polygon :: [Vertex] - Region

Shape.Polygon is a qualified name, and you probably have a module
called Shape. Use spaces around the dot ...

Cheers,
  Andres
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Re: help from the community?

[Andres Loeh]

 Just a little remark on the side: 'If' and 'case' demand exactly one
 expression. In such cases allowing zero expressions is not a
 generalization but an unnecessary complication. 'Let' and 'where'
 allow any number of bindings, so allowing zero bindings (instead of
 demanding at least one) is a simplification.
 
 I meant the branches of a case (the report specifies at least 1).
 
 I think it's important to keep some possibility for the compiler to detect 
 probable errors as syntax errors. If all syntax is inhabited by strange 
 defaults then this just means simple errors will go undetected eg:
 
let a = case foo of
 
 Here, the user has probably got sidetracked into editing some other part of 
 the program and just forgotten to get back to fill in the cases for the 
 case construct. Allowing zero cases means the user will get a strange 
 runtime error instead as the function part of the case is undefined.

I agree. On the other hand, if there are uninhabited types (modulo _|_), it
might be nice to have an empty case as an explicit eliminator.

let z = \y (foo y)
 
 Here, it seems clear that the user has just forgotten to type the - which 
 means a simple syntax error would get transformed into a much more puzzling 
 (esp for a newbie) type error.

Again, for the lambda I obviously meant the case of 0 variables, i.e. something
like (\ - y) which would then just be equivalent to y. I think this case is
probably the one that's most comparable to the situation in question (whether
to allow empty forall's). Since the designers of previous Haskell versions
obviously thought it's a good idea to disallow empty lambdas, let's disallow
empty forall's as well.

Cheers,
  Andres
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Re: help from the community?

[Andres Loeh]

  The only reasons that I could see in favor of allowing empty foralls
  is that it might be easier to automatically generate code. Haskell
  seems to be a bit inconsistent in how it treats empty constructs. For
  example, empty let and empty where seems to be allowed, but not an
  empty case?
 
 Just a little remark on the side: 'If' and 'case' demand exactly one
 expression. In such cases allowing zero expressions is not a generalization
 but an unnecessary complication. 'Let' and 'where' allow any number of
 bindings, so allowing zero bindings (instead of demanding at least one) is
 a simplification.

I meant the branches of a case (the report specifies at least 1). Similarly,
the report specifies that lambdas must have at least one argument, infix
declarations must not be empty and datatype declarations must not be empty
(the latter will definitely be fixed).

Cheers,
  Andres
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Re: help from the community?

[Andres Loeh]

 I cannot see how an empty list of tyvars is useful or desirable in
 practice:
 data Foo = Foo (forall . Int)
 is equivalent to just
 data Foo = Foo Int
 so why bother to permit the former?  It probably indicates some error in
 the thinking of the programmer, so the compiler should bring it to her
 attention.

The only reasons that I could see in favor of allowing empty foralls
is that it might be easier to automatically generate code. Haskell
seems to be a bit inconsistent in how it treats empty constructs. For
example, empty let and empty where seems to be allowed, but not an
empty case?

 On the other hand, I can imagine a use for phantom type variables in the
 quantifier (especially if they occur in multi-parameter predicates, but
 not in the type).  So I think accepting them with a warning is
 reasonable.
 
 I can also imagine predicates that do not mention locally-quantified
 variables - the assumption must be that they mention variables bound on
 the LHS of the datatype decl instead?  e.g. the Show predicate here:
 
 data Foo a b = Foo a b
  | Bar (forall c . (Show b, Relation b c) = (b,c))
 
 Hmm, maybe a simpler version of this example would illustrate what you
 mean by the proposal (first of the three bullets) to allow an empty
 quantifier list:
 
 data Foo a b = Foo a b
  | Bar (forall . Show b = b)
 
 In which case, does this even count as a polymorphic component at all?
 Is it not rather GADT-like instead?
 
 data Foo a b where
   Foo :: a - b - Foo a b
   Bar :: Show b = b - Foo a b

Would these two have the same meaning? I have a feeling what the GADT
is, but no idea what the former type means.

  Constructor that have polymorphic components cannot appear in the
  program without values for their polymorphic fields.
 
 I didn't fully understand this requirement.  If Haskell-prime gets
 rank-2 or rank-n types, then do we need to restrict constructors in this
 way?

Ok, this really boils down to the question of whether we do rank-2 or
rank-n types. I'm biased, because I actually use rank-n types
frequently, and feel somewhat limited by the rank-2 restrictions.  I
don't know how many people actually do, though. I can understand
Iavor's points that rank-2 might be easier to explain, but at least
GHC's rank-n extension has a very detailed paper explaining it, so I
guess it's one of the better documented extensions.

I very much agree that nested patterns for polymorphic components
should be disallowed.

Cheers,
  Andres
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Re: recent changes to draft haskell prime report

[Andres Loeh]

 I have fiddled with the build system, to enable the current state of the
 Report in the darcs repository to be generated into (at least) HTML,
 (hopefully also PDF and PS soon) automatically as every patch is checked

do we still need PS?

 in.  In theory, the following link should always give you the most
 up-to-date version of the text:
 
 http://darcs.haskell.org/haskell-prime-report/report/haskell-prime-draft.html
 
 (I am wondering whether to make this a 'darcs test' thing, so if the
 Report fails to build, your patch will be rejected.  Any opinions?)

Good idea.

Cheers,
  Andres
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[Haskell] ANNOUNCE: lhs2tex-1.12

[Andres Loeh]

 lhs2TeX version 1.12
 

We are pleased to announce a new release of lhs2TeX, 
a preprocessor to generate LaTeX code from literate Haskell
sources.

lhs2TeX includes the following features:

* Highly customized output.

* Liberal parser -- no restriction to Haskell 98.

* Generate multiple versions of a program or document from 
  a single source.

* Active documents: call Haskell to generate parts of the 
  document (useful for papers on Haskell).

* A manual explaining all the important aspects of lhs2TeX.

Changes (w.r.t. lhs2TeX 1.11)
-

* Compatible with ghc-6.6.

* Compatible with cabal-1.1.6; traditional configure/make
  installation should still work. Thanks to Brian Smith
  for submitting a patch to improve the Cabal experience
  on Windows.

Requirements and Download
-

A source distribution is available from

  http://www.iai.uni-bonn.de/~loeh/lhs2tex/

It has been verified to build on Linux and MacOSX, but
should also work on Windows. Binaries will be made available
on request.

You need a recent version of GHC (6.4.2 is tested, older versions
might work) to build lhs2TeX, and, of course, you need a TeX
distribution to make use of lhs2TeX's output. The program includes
a configuration that is suitable for use with LaTeX. In theory, 
there should be no problem to generate code for other TeX 
flavors, such as plainTeX or ConTeXt.


  Happy lhs2TeXing,
  Andres Loeh and Ralf Hinze

  [EMAIL PROTECTED]
  [EMAIL PROTECTED]
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[Haskell] ANNOUNCE: Haskell Communities Activities Report (11th ed., November 2006)

[Andres Loeh]

On behalf of the many, many contributors, I am pleased to announce
that the

  Haskell Communities and Activities Report
(11th edition, November 2006)

 http://www.haskell.org/communities/

is now available from the Haskell Communities home page in several
formats: PDF, for screenreading as well as printing, HTML, for those 
of you who prefer not to deal with plugins or external viewers, and 
PostScript, for those of you who have nice quick printers that do not 
grok PDF.

Many thanks go to all the people that contributed to this report,
both directly, by sending in descriptions, and indirectly, by doing
all the interesting things that are reported. I hope you will find
it as interesting a read as we did.

If you haven't encountered the Haskell Communities and Activities 
Reports before, you may like to know that the first of these reports
was published in November 2001. Their goal is to improve the 
communication between the increasingly diverse groups, projects and
individuals working on, with, or inspired by Haskell. The idea behind
these reports is simple:

Every six months, a call goes out to all of you enjoying Haskell to
contribute brief summaries of your own area of work. Many of you 
respond (eagerly, unprompted, and well in time for the actual 
deadline ;) ) to the call. The editor collects all the contributions 
into a single report and feeds that back to the community.

When we try for the next update, six months from now, you might want 
to report on your own work, project, research area or group as well.
So, please put the following into your diaries now:


   End of April 2007:
target deadline for contributions to the
  May 2006 edition of the HCA Report


Unfortunately, many Haskellers working on interesting projects are so
busy with their work that they seem to have lost the time to follow
the Haskell related mailing lists and newsgroups, and have trouble even
finding time to report on their work. If you are a member, user or 
friend of a project so burdened, please find someone willing to make 
time to report and ask them to `register' with the editor for a simple 
e-mail reminder in the middle of April (you could point me to them as 
well, and we can then politely ask if they want to contribute, but it 
might work better if you do the initial asking). Of course, they will
still have to find the ten to fifteen minutes to draw up their report,
but maybe we can increase our coverage of all that is going on in the
community.

Feel free to circulate this announcement further in order to
reach people who might otherwise not see it. Enjoy!

Andres Loeh 
hcar at haskell.org

-- 
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[Haskell] REMINDER: HCA Report (November 2006 edition)

[Andres Loeh]

Dear Haskellers,

the deadline for the November 2006 edition of the Haskell Communities
and Activities Report is only a few days away -- but this is still
enough time to make sure that the report contains a section on *your*
project, on the interesting stuff that you've been doing; using or
affecting Haskell in some way.

Many projects that have been included in former reports have not yet
updated their entries. Please have a look at the June 2006 edition
for reference.

* Has your project been listed in previous Reports, but is not yet
  updated? Please write a short update!

* Are you no longer working on a project that was included in the
  Report? Write up what you are working on instead, and tell me if
  someone else has picked up the project.

* Is some project you have heard about not included in any previous
  Report? Please let me know ...

There is still time to write a completely new entry, on a new
compiler, tool, library, company, user group, idea, ... -- as long as
there is a connection to the Haskell language, there is a place for it
in the Report!

The general deadline is

  Monday, 06 November 2006,

but I can extend it by a few days on an individual basis. Just please
contact me before the deadline so that I know you are writing.

Please mail your entries to hcar at haskell dot org, in plain text
or pseudo-(La)TeX format. More information can be found in the
original Call for Contributions at

  http://www.haskell.org/pipermail/haskell/2006-October/018646.html

I look forward to receiving your contributions.

Thanks a lot,

  Andres (current editor)

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[Haskell] Call for Contributions - HCA Report (November 2006 edition)

[Andres Loeh]

Dear Haskellers,

it is nearly time for the eleventh edition of the

  
  Haskell Communities  Activities Report  
http://www.haskell.org/communities/

   Submission deadline:  6 November 2006

  (please send your contributions to hcar at haskell.org, in 
plain ASCII or LaTeX format)
  

This is the short story:

* If you are working on any project that is in some way related
  to Haskell, write a short entry and submit it to the me.

* If you are interested any project related to Haskell that has not 
  previously been mentioned in the HCA Report, please tell me, so 
  that I can contact the project leaders and ask them to submit
  an entry.

* Feel free to pass on this call for contributions to others that
  might be interested.

More detailed information:

The Haskell Communities  Activities Report is a bi-annual overview of
the state of Haskell as well as Haskell-related projects over the
last, and possibly the upcoming 6 months. If you have only recently
been exposed to Haskell, it might be a good idea to browse the 
June 2006 edition -- you will find interesting topics described as well
as several starting points and links that may provide answers to many
questions.

Contributions will be collected until the beginning of November. They
will be compiled into a coherent report which will appear sometime
near the end of November. As always, this is a great opportunity to
update your webpages, make new releases, announce of even start new
projects, or to point at some developments you want every Haskeller to
see!

As the purpose of the report is to collect recent or current
activities, I encourage you to update all existing summaries and
reports. I will probably drop any topics that have not had any
activity for the past year, i.e., since November 2005, but I would
very much prefer you to present an updated description of the
topic. Of course, new entries are more than welcome.  Reports should
generally be kept brief and informative, ranging from a few sentences
to a few hundred words, to keep the whole report reasonably sized.

Looking forward to your contributions,

Andres (current editor)

--- topics

New suggestions for current hot topics, activities, projects, etc.
are welcome - especially with names and addresses of potential
contacts, but here is a non-exclusive list of likely topics
(see also http://www.haskell.org/communities/topics.html ):

General Haskell developments
  Haskell implementations
  Haskell extensions
  Standardization (Haskell', ...)
  Documentation
  Libraries
  Papers and Books

Feedback
  Summaries of discussions in specialist mailing lists
  Conference reports
  Community activities
  Other Haskell information channels (TMR, Sequence, HWN, ...)

Announcements
  Upcoming Haskell events
  Everything that's new or has had new releases

Ongoing projects
  Reports on what's happening behind the scenes
  Confirmations that projects are still maintained
  Calls for contributions and contributors

Tutorials

Tools and Applications
  Released and unreleased Haskell applications
  Tools useful for Haskell programmers 
  Experiences with using Haskell for a project
  Commercial uses of Haskell

Even if your topic is not listed in this list, there's a good chance
it has a place in the Report. Please get in touch with me.

If you want to see an entry that hasn't been there in the past, but
you are not the maintainer of the project, then please encourage the
maintainers to write an entry/update, or ask permission to write the
entry yourself.

-- what should I write?

That depends on your topic, but as a general rule, it shouldn't take
you long. A simple sentence or two about your use of Haskell could
go into the Individual Haskellers section. If you're a company, 
or if you're working on a project using Haskell as the implementation
language, a paragraph on that could go into the Applications section.

A typical summary report about a tool/library/project/application/...
would be between 1 and 3 paragraphs of ASCII text (what's it about? 
major topics and results since the last report?  current hot topics?
major goals for the next six months?) plus pointers to material for
further reading (typically to a home page, or to mailing list  
archives, specifications and drafts, implementations, meetings,
minutes, ...).

Browsing through previous editions should give you a good idea of
the variety of possibilities, ranging from very brief to extensive. 

For those who prefer templates to fill in, the report is edited in  
LaTeX, and an entry template might look something like this:

\begin{hcarentry}{(MYSTUFF)}
\report{(MY NAME)}
\status{(PROJECT STATUS IN ONE LINE)}
\participants{(PARTICIPANTS OTHER THAN MYSELF)}% optional
\makeheader

Re: writing / status teams - call for volunteers

[Andres Loeh]

 Would anyone else like to volunteer to write a section of the report for
 specific proposals below?
 
  In
  ==
  
  #74: add some kind of concurrency: SM, HN, IJ
  #35: add ForeignFunctionInterface: MC, SM
  #49: add multi parameter type classes: MS
  #60: add RankNTypes or Rank2Types: AL
  #57: add polymorphic components: AL
  #26: add ExistentialQuantification (existential components): AL, MS, SJT
  #24: add HierarchicalModules: BH, IJ
  #25: add EmptyDataDeclarations: BH, HN
  #23: fix common pitfall with the do-notation and if-then-else: SM, HN, 
  #42: fix comment syntax grammar: SM
  #56: add Pattern Guards: :(
  #78: Add infix type constructors: BH, AL
  Help w/ libraries (yay!): IJ, BH, SM, RP, DS

I would like to start writing a new section on the syntax of data type
declarations. All the proposals I've put my name on are somewhat related
to this area, most of all existential quantification and infix type
constructors.

Have we already discussed how we produce new text for the report? Is this
supposed to be all on the Wiki, or are we going to modify the TeX sources
of the Haskell-98 report? Is the plan to keep the general style and structure
of the Haskell-98 report, or are we going to rewrite and restructure the
whole report?

Cheers,
  Andres
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Re: Exceptions

[Andres Loeh]

Hi Ashley.

Thanks for your interest in open data types. As one of the authors of
the open data types paper, I'd like to comment on the current
discussion.

You comment Simon's upcoming HW paper on extensible exceptions:

 You write:
 
  Compared to our approach, theirs requires new extensions to the language 
  (although not deep),
 
 Typeable is an extension to Haskell, and a rather ugly one at that. 
 The open datatypes extension is both cleaner and more general.

I think the stress here is on *new* extensions. I agree that an open
type of type representations might be a more beautiful solution to the
problem that Typeable solves. Nevertheless, the fact is that Simon's
solution can be used in current GHC without further implementation work.

  and has difficulties with separate compilation.
 
 They claim to solve this I think, though I haven't examined it really 
 carefully. You may know better, of course.

I've discussed this with Simon PJ. Apart from minor technical problems,
everything seems doable in GHC, but it is quite some work and it's not clear
that I will have the time to study GHC closely enough to do it in the
near future. I hope I can say more after the Hackathon ...

  Arguably the open data types approach is more direct and more accessible,
 
 Yes,
 
  as is often the case with extensions designed to solve a particular problem.
 
 That's not fair. Open datatypes have other applications. A general file 
 interpreter for instance, that given a MIME type string and a list of 
 bytes yields an object. Or a collection of variable resources of 
 various types that could be passed to a program. Or a hierarchy of UI 
 widgets. Or anything that Typeable and Dynamic are currently used for, 
 but more cleanly. Hs-plugins, for instance.
 
 It's the missing piece.

True, open data types have never been invented as a solution to the
problem of extensible exceptions. It is an application that we found
afterwards.

  Still, the argument for adding open data types to the language is weakened 
  by 
  the fact that they are subsumed by type classes: in fact the authors give 
  an 
  encoding of open data types into type classes,
 
 Well not really. The encoding involves lifting everything from values 
 to types, which means a function still can't return a value of an open 
 type determined at run-time.

Even if both approaches would be equally expressive, the type class encoding
still has a lot of syntactic overhead. Moving from a closed to an open data
type encoded by type classes requires changing your whole program, whereas
with open data types, it is a local change.

Apart from this discussion however, open data types are clearly not
Haskell' material, because the proposal is new and currently
unimplemented.

The extensions required for Simon's approach to exceptions have a good
chance of being included in Haskell'.

Cheers,
  Andres
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[Haskell] Haskell Workshop 2006 Call for participation

[Andres Loeh]

Please note that the early registration deadline is August 18, 2006.

Cheers,
  Andres

---

 ACM SIGPLAN 2006 Haskell Workshop
   Call for Participation

  Portland, Oregon
 Sunday, September 17, 2006

---

   The Haskell Workshop 2006 will be part of the 2006 International
   Conference on Functional Programming (ICFP).

   The purpose of the Haskell Workshop is to discuss experience with
   Haskell, and possible future developments for the language. The scope
   of the workshop includes all aspects of the design, semantics, theory,
   application, implementation and teaching of Haskell.

Preliminary Schedule

   08:25 Welcome


   Session I

   08:30 Stephanie Weirich (University of Pennsylvania)
 RepLib: A Library for Derivable Type Classes

   09:00 Deling Ren and Martin Erwig (Oregon State University)
 A Generic Recursion Toolbox for Haskell
(Or: Scrap Your Boilerplate Systematically)

   09:30 Alexandra Silva (CWI, The Netherlands)
and Joost Visser (Universidade do Minho, Portugal)
 Strong Types for Relational Databases (Functional Pearl)


   10:00 Break


   Session II

   10:30 Koji Kagawa (RISE, Kagawa University)
 Polymorphic Variants in Haskell

   11:00 Dana N. Xu (University of Cambridge)
 Extended Static Checking for Haskell

   11:30 Philip Derrin, Kevin Elphinstone, Gerwin Klein, David Cock and
Manuel M.T. Chakravarty (University of New South Wales)
 Running the Manual: An Approach to High-Assurance
Microkernel Development

   12:00 Iavor S. Diatchki (OGI) and
Mark P. Jones (Portland State University)
 Strongly Typed Memory Areas -- Programming Systems-Level
Data Structures in a Functional Language


   12:30 Lunch


   Session III

   14:00 Peter Thiemann (Universität Freiburg)
 User-Level Transactional Programming in Haskell

   14:30 Simon Marlow (Microsoft Research)
 An Extensible Dynamically-Typed Hierarchy of Exceptions

   15:00 David Himmelstrup (Denmark)
 Demo: Interactive Debugging with GHCi

   15:15 Andy Gill (Galois Connections)
 Demo: Introducing the Haskell Equational Reasoning Assistant


   15:30 Break


   Session IV

   16:00 Program Chair Report

   16:15 Eric Kow (LORIA)
 GenI: Natural Language Generation in Haskell

   16:45 Frederik Eaton
 Demo: Typed Linear Algebra

   17:00 Isaac Jones (Galois Connections)
 Haskell' Status Report -- An Update on the
Next Haskell Standard


   Session V

   17:15 Discussion: The Future of Haskell


Program Committee

   Koen Claessen, Chalmers University, Sweden
   Bastiaan Heeren, Universiteit Utrecht, The Netherlands
   Paul Hudak, Yale University, US
   Isaac Jones, Galois Connections, US
   Gabriele Keller, University of New South Wales, Australia
   Oleg Kiselyov, FNMOC, US
   Andres Loeh (chair), Universitaet Bonn, Germany
   Conor McBride, University of Nottingham, UK
   Shin-Cheng Mu, Academia Sinica, Taiwan
   Andrew Tolmach, Portland State University, US
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Re: [Haskell] ANNOUNCE: HNOP 0.1

[Andres Loeh]

 Could you perhaps write a Haskell Weekly News entry for this? It might
 also be worth contacting Andres Löh and seeing if we can get a late
 entry into the Haskell Communities and Activities Report, this seems
 critical enough.

I agree that it is pretty critical, but I'll rather do a HNOP this
time, and instead give it a prominent position in the November edition
(if I receive a project report).

Cheers,
  Andres
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[Haskell] ANNOUNCE: Haskell Communities Activities Report (10th ed., June 2006)

[Andres Loeh]

On behalf of the many, many contributors, I am pleased to announce
that the

  Haskell Communities and Activities Report
 (10th edition, June 2006)

 http://www.haskell.org/communities/

is now available from the Haskell Communities home page in several
formats: PDF, for screenreading as well as printing, HTML, for those 
of you who prefer not to deal with plugins or external viewers, and 
PostScript, for those of you who have nice quick printers that do not 
grok PDF.

Many thanks go to all the people that contributed to this report,
both directly, by sending in descriptions, and indirectly, by doing
all the interesting things that are reported. I hope you will find
it as interesting a read as we did.

If you haven't encountered the Haskell Communities and Activities 
Reports before, you may like to know that the first of these reports
was published in November 2001. Their goal is to improve the 
communication between the increasingly diverse groups, projects and
individuals working on, with, or inspired by Haskell. The idea behind
these reports is simple:

Every six months, a call goes out to all of you enjoying Haskell to
contribute brief summaries of your own area of work. Many of you 
respond (eagerly, unprompted, and well in time for the actual 
deadline ;) ) to the call. The editor collects all the contributions 
into a single report and feeds that back to the community.

When we try for the next update, six months from now, you might want 
to report on your own work, project, research area or group as well.
So, please put the following into your diaries now:


  End of October 2006:
target deadline for contributions to the
November 2006 edition of the HCA Report


Unfortunately, many Haskellers working on interesting projects are so
busy with their work that they seem to have lost the time to follow
the Haskell related mailing lists and newsgroups, and have trouble even
finding time to report on their work. If you are a member, user or 
friend of a project so burdened, please find someone willing to make 
time to report and ask them to `register' with the editor for a simple 
e-mail reminder in the middle of October (you could point me to them as 
well, and we can then politely ask if they want to contribute, but it 
might work better if you do the initial asking). Of course, they will
still have to find the ten to fifteen minutes to draw up their report,
but maybe we can increase our coverage of all that is going on in the
community.

Feel free to circulate this announcement further in order to
reach people who might otherwise not see it. Enjoy!

Andres Loeh 
hcar at haskell.org

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Re: [Haskell] REMINDER: HCA Report (extended deadline: 15 May 2006)

[Andres Loeh]

 If you would extend the deadline to sometime after May 23, when the
 accepted Haskell.org SoC applications are revealed, you could perhaps get
 a lot of new projects to the list.

I would rather not do this. It is already later than in the previous
years for the May edition, and due to other commitments, I definitely
want to get the Report released before the end of May (and it usually
needs at least a week, if not more, after the deadline, to go through
all the submissions).

The next Report is already in November, and will be a perfect
opportunity to report on all the SoC projects.

For this issue, I would propose that someone writes a summary of
haskell.org's SoC participation (please!), which could possibly
include a list of the accepted projects (I don't think it would be a
problem to include such a list on very short notice into an already
submitted article, and it is unlikely that the Report will actually
appear before May 23 for the abovementioned reasons).

Cheers,
  Andres
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[Haskell] REMINDER: HCA Report (extended deadline: 15 May 2006)

[Andres Loeh]

Dear Haskellers,

the deadline for the May 2006 edition of the Haskell Communities
and Activities Report is only a few days away -- but this is still
enough time to make sure that the report contains a section on *your*
project, on the interesting stuff that you've been doing; using or
affecting Haskell in some way.

Many projects that have been included in former reports have not yet
updated their entries. Please have a look at the November 2005 edition
for reference.

* Has your project been listed in previous Reports, but is not yet
  updated? Please write a short update!

* Are you no longer working on a project that was included in the
  Report? Write up what you are working on instead, and tell me if
  someone else has picked up the project.

* Is some project you have heard about not included in any previous
  Report? Please let me know ...

There is still time to write a completely new entry, on a new
compiler, tool, library, company, user group, idea, ... -- as long as
there is a connection to the Haskell language, there is a place for it
in the Report!

I have slightly extended the deadline. Submissions are now due by next
Monday, that is

  15 May 2006.

Please mail your entries to hcar at haskell dot org, in plain text
or pseudo-(La)TeX format. More information can be found in the
original Call for Contributions at

  http://www.haskell.org/pipermail/haskell/2006-April/017861.html

I look forward to receiving your contributions.

Thanks a lot,

  Andres (current editor)

-- 
Haskell Communities and Activities Report (http://haskell.org/communities)
05/2006 edition extended submission deadline: 15 May 2006 [EMAIL PROTECTED]
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[Haskell] Haskell Workshop 2006 Second call for papers

[Andres Loeh]

Apologies for multiple copies; feel free to distribute further.

Cheers,
  Andres

 ACM SIGPLAN 2006 Haskell Workshop
  Call for Papers

  Portland, Oregon
 17 September, 2006


   The Haskell Workshop 2006 will be part of the 2006 International
   Conference on Functional Programming (ICFP) as an associated, ACM
   SIGPLAN sponsored workshop. Previous Haskell Workshops have been held
   in La Jolla (1995), Amsterdam (1997), Paris (1999), Montreal (2000),
   Firenze (2001), Pittsburgh (2002), Uppsala (2003), Snowbird (2004),
   and Tallinn (2005).

Topics

   The purpose of the Haskell Workshop is to discuss experience with
   Haskell, and possible future developments for the language. The scope
   of the workshop includes all aspects of the design, semantics, theory,
   application, implementation, and teaching of Haskell. Topics of
   interest include, but are not limited to, the following:
 * Language Design, with a focus on possible extensions and
   modifications of Haskell as well as critical discussions of the
   status quo;
 * Theory, in the form of a formal treatment of the semantics of the
   present language or future extensions, type systems, and
   foundations for program analysis and transformation;
 * Implementations, including program analysis and transformation,
   static and dynamic compilation for sequential, parallel, and
   distributed architectures, memory management as well as foreign
   function and component interfaces;
 * Tools, in the form of profilers, tracers, debuggers,
   pre-processors, and so forth;
 * Applications, Practice, and Experience with Haskell for scientific
   and symbolic computing, database, multimedia and Web applications,
   and so forth as well as general experience with Haskell in
   education and industry;
 * Functional Pearls being elegant, instructive examples of using
   Haskell.

   Papers in the latter two categories need not necessarily report
   original research results; they may instead, for example, report
   practical experience that will be useful to others, re-usable
   programming idioms, or elegant new ways of approaching a problem. The
   key criterion for such a paper is that it makes a contribution from
   which other practitioners can benefit. It is not enough simply to
   describe a program!

Submission details

   Submission deadline: Friday, 2 June 2006 (23:00 Samoa standard time, UTC -11)
   Notification:Monday, 3 July 2006

   Authors should send their papers
   to Andres Loeh ([EMAIL PROTECTED]) by e-mail. Submitted
   papers should be in (postscript or) portable document format,
   formatted using the ACM SIGPLAN style guidelines. Papers should not
   exceed 12 pages in length.

   Accepted papers will be published by the ACM and will appear in the
   ACM Digital Library.

   If there is sufficient demand, we will try to organise a time slot for
   system or tool demonstrations. If you are interested in demonstrating
   a Haskell related tool or application, please send a brief demo
   proposal to Andres Loeh ([EMAIL PROTECTED]).

Programme Committee

   Koen Claessen, Chalmers University, Sweden
   Bastiaan Heeren, Universiteit Utrecht, The Netherlands
   Paul Hudak, Yale University, US
   Isaac Jones, Galois Connections, US
   Gabriele Keller, University of New South Wales, Australia
   Oleg Kiselyov, FNMOC, US
   Andres Loeh (chair), Universitaet Bonn, Germany
   Conor McBride, University of Nottingham, UK
   Shin-Cheng Mu, Academia Sinica, Taiwan
   Andrew Tolmach, Portland State University, US

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[Haskell] Re: haskell.org libraries and tools page needs some fixing

[Andres Loeh]

 BB I recently wanted to add some libraries to
 BB http://www.haskell.org/haskellwiki/Libraries_and_tools and noticed a 
 BB number of problems.
 
 there is also HCAR report. my thoughts is what we should create some
 central repository including libs/apps/papers/communities and so on
 and replace both this page and HCAR with it. then anyone should
 include himself here and edit the info as progress does. 

Such a proposal comes up every once in a while, and it certainly
sounds like a good idea. But I don't think it will work. From my
experience, getting a HCAR done is not only a lot of fun, but also
quite a bit of work. I think that it is a good thing to have a fixed
point in time when people involved in the Haskell community are
actively approached and asked and pushed to write up what they have
done. In the HCAR, you can see for every single entry if it has been
updated or not (and stuff that is outdated is removed). The result is
archived as a stable point of reference.  With a central repository,
chances are good that no one really feels responsible, and it will be
difficult to reach the same level of breadth and quality. You
certainly can get rid of these advantages by assigning an editor and
some rules ... but why, really, do you want to replace the HCAR with
anything? What do you dislike about it?

Cheers,
  Andres
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[Haskell] ANNOUNCE: lhs2tex-1.11

[Andres Loeh]

 lhs2TeX version 1.11
 

We are pleased to announce a new release of lhs2TeX, 
a preprocessor to generate LaTeX code from literate Haskell
sources.

lhs2TeX includes the following features:

* Highly customized output.

* Liberal parser -- no restriction to Haskell 98.

* Generate multiple versions of a program or document from 
  a single source.

* Active documents: call Haskell to generate parts of the 
  document (useful for papers on Haskell).

* A manual explaining all the important aspects of lhs2TeX.

Changes (w.r.t. lhs2TeX 1.9)


[Note that 1.10 has never been released to avoid confusion
with some privately distributed versions.] 

* Specification code is now handled correctly (that is, ignored) 
  in the code and newcode styles.

* Comments and Pragmas are handled in a better way by 
  the newcode style.

* There are some new forms of implicit formatting directives.

* The LaTeX code produced in the poly style looks slightly
  more beautiful.

* There is a new Library section, containing some frequently
  used formatting directives.

* Generation of file/linenumber directives in the produced
  LaTeX code, for Stefan Wehr's adjust tool. Based on a
  patch submitted by Stefan Wehr.

* lhs2TeX can now replace ghc's literate preprocessor.

* Improved efficiency of \eval and \perform (to call ghci
  or hugs from lhs2TeX documents).

Requirements and Download
-

A source distribution that should be suitable for Unix-based
environments is available from

  http://www.iai.uni-bonn.de/~loeh/lhs2tex/

It has been verified to build on Linux and MacOSX.
Binaries will be made available on request.

You need a recent version of GHC (6.4.1 is tested, 6.2.2 might
work) to build lhs2TeX, and, of course, you need a TeX distribution 
to make use of lhs2TeX's output. The program includes a 
configuration that is suitable for use with LaTeX. In theory, 
there should be no problem to generate code for other TeX 
flavors, such as plainTeX or ConTeXt.


  Happy lhs2TeXing,
  Andres Loeh and Ralf Hinze

  [EMAIL PROTECTED]
  [EMAIL PROTECTED]
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Re: [Haskell-cafe] Decidable type systems? (WAS: Associated Type Synonyms question)

[Andres Loeh]

 Can someone explain to me why decidability is of any practical interest 
 at all? What's the (practical) difference between a decision procedure 
 which might never terminate and one which might take 1,000,000 years to 
 terminate? Actually, why push it out to 1,000,000 years: in the context 
 of a compiler for a practical programming language, a decision 
 procedure which might take an hour to terminate might as well be 
 undecidable ... surely all we really need is that the decision 
 procedure _typically_ terminates quickly, and that where it doesn't we 
 have the means of giving it hints which ensure that it will.

I'm tempted to agree with you. I don't care if the compiler terminates
on all my programs, or if it sometimes quits and says: I don't know if
this is correct. However, I do think that it is of very much importance
that programmers and compiler implementors know which programs are legal
and which are not.

If a problem is decidable, it has the nice property that the problem
(*not* the algorithm) can be used as a specification. Implementors are
free to implement different algorithms, as long as they all solve the
problem. If the problem is undecidable, how do you make sure that different
compilers accept the same programs? If you don't want to find a subproblem
that is decidable, you'll have to specify an algorithm, which is usually
far more complicated, error-prone, and difficult to grasp for programmers.

Cheers,
  Andres
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[Haskell] Haskell Workshop 2006 Call for papers

[Andres Loeh]

Apologies for multiple copies; feel free to distribute further.

Cheers,
  Andres

 ACM SIGPLAN 2006 Haskell Workshop
  Call for Papers

  Portland, Oregon
 17 September, 2006


   The Haskell Workshop 2006 will be part of the 2006 International
   Conference on Functional Programming (ICFP) as an associated, ACM
   SIGPLAN sponsored workshop. Previous Haskell Workshops have been held
   in La Jolla (1995), Amsterdam (1997), Paris (1999), Montreal (2000),
   Firenze (2001), Pittsburgh (2002), Uppsala (2003), Snowbird (2004),
   and Tallinn (2005).

Topics

   The purpose of the Haskell Workshop is to discuss experience with
   Haskell, and possible future developments for the language. The scope
   of the workshop includes all aspects of the design, semantics, theory,
   application, implementation, and teaching of Haskell. Topics of
   interest include, but are not limited to, the following:
 * Language Design, with a focus on possible extensions and
   modifications of Haskell as well as critical discussions of the
   status quo;
 * Theory, in the form of a formal treatment of the semantics of the
   present language or future extensions, type systems, and
   foundations for program analysis and transformation;
 * Implementations, including program analysis and transformation,
   static and dynamic compilation for sequential, parallel, and
   distributed architectures, memory management as well as foreign
   function and component interfaces;
 * Tools, in the form of profilers, tracers, debuggers,
   pre-processors, and so forth;
 * Applications, Practice, and Experience with Haskell for scientific
   and symbolic computing, database, multimedia and Web applications,
   and so forth as well as general experience with Haskell in
   education and industry;
 * Functional Pearls being elegant, instructive examples of using
   Haskell.

   Papers in the latter two categories need not necessarily report
   original research results; they may instead, for example, report
   practical experience that will be useful to others, re-usable
   programming idioms, or elegant new ways of approaching a problem. The
   key criterion for such a paper is that it makes a contribution from
   which other practitioners can benefit. It is not enough simply to
   describe a program!

Submission details

   Submission deadline: 2 June 2006
   Notification:3 July 2006

   Submitted papers should be in postscript or portable document format,
   formatted using the ACM SIGPLAN style guidelines. The length
   should be restricted to 12 pages.

   Detailed submission instructions will be available at
   http://haskell.org/haskell-workshop/2006.

   Accepted papers will be published by the ACM and will appear in the
   ACM Digital Library.

   If there is sufficient demand, we will try to organise a time slot for
   system or tool demonstrations. If you are interested in demonstrating
   a Haskell related tool or application, please send a brief demo
   proposal to Andres Loeh ([EMAIL PROTECTED]).

Programme Committee

   Koen Claessen, Chalmers University, Sweden
   Bastiaan Heeren, Universiteit Utrecht, The Netherlands
   Paul Hudak, Yale University, US
   Isaac Jones, Galois Connections, US
   Gabriele Keller, University of New South Wales, Australia
   Oleg Kiselyov, FNMOC, US
   Andres Loeh (chair), Universitaet Bonn, Germany
   Conor McBride, University of Nottingham, UK
   Shin-Cheng Mu, Academia Sinica, Taiwan
   Andrew Tolmach, Portland State University, US

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Re: Parallel list comprehensions

[Andres Loeh]

 I noticed ticket #55--add parallel list comprehensions--which according to
 the ticket, will probably be adopted. I would argue against.

[Several good points removed.]

I agree.

Cheers,
  Andres
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Re: Bugs with GADTs in GHC6.4.1

[Andres Loeh]

 The attached script induces panic in GHC6.4.1: ghc-6.4.1: panic! (the 
 `impossible' happened, GHC version 6.4.1): applyTypeToArgs f{v a1Eg} 
 x{v a1Ei}.

I think this is related to a known bug, because the same workaround
helps -- annotate the f and x arguments in the last line of your
program with dummy type variables, and the program will be accepted:

 zap :: Vector n (a - b) - Vector n a - Vector n b
 zap fs xs = unfoldv f (len fs) (VP (fs, xs)) where
   f :: VectorPair (a-b) a (S n) - (b, VectorPair (a-b) a n)
   f (VP (VCons (f :: foo) fs, VCons (x :: bar) xs)) = (f x, VP (fs, xs))

Cheers,
  Andres
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Re: bug in GADT typechecking

[Andres Loeh]

  {-# OPTIONS_GHC -fglasgow-exts #-}
  module Main where
  
  data Foo a b where
  Foo :: Int - Foo a b
  
  data Patch a b where
  PP :: Foo a b - Patch a b
  Lis :: PL a b - Patch a b
  
  data PL a b where
  U :: Patch a b - PL a b
  Nil :: PL x x
  (:-) :: PL c d - PL d e - PL c e
  
  data Pair alpha omega where
  (:.) :: Patch a i - Patch i o - Pair a o
  
  foo :: Pair a b - Maybe (Pair a b)
  foo (Lis (U x :- y) :. Lis Nil) = Just (PP x :. Lis y)
 
   
 
 Oddly enough, the code *does* typecheck if we change the above line to
 
 foo (Lis (U a :- b) :. Lis Nil) = Just (Lis (U a) :. Lis b)
 
 which differs only in here   

Looks to me as if ghc is right to complain. PP takes a Foo, but U takes
a Patch. Therefore the x that's matched on the lhs is a Patch, not a Foo.

 test.lhs:27:44:
 Couldn't match `Foo a b' against `Patch a1 d'
   Expected type: Foo a b
   Inferred type: Patch a1 d
 In the first argument of `PP', namely `x'
 In the first argument of `(:.)', namely `PP x'

 Glasgow Haskell Compiler, Version 6.4, for Haskell 98, compiled by GHC 
 version 6.4

FWIW, same error with ghc-6.5 from a few weeks ago.

Cheers,
  Andres
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[Haskell] ANNOUNCE: Haskell Communities Activities Report (9th ed., November 2005)

[Andres Loeh]

On behalf of the many, many contributors, I am pleased to announce
that the

  Haskell Communities and Activities Report
(9th edition, November 2005)

 http://www.haskell.org/communities/

is now available from the Haskell Communities home page in several
formats: PDF, for screenreading as well as printing, HTML, for those 
of you who prefer not to deal with plugins or external viewers, and 
PostScript, for those of you who have nice quick printers that do not 
grok PDF.

Many thanks go to all the people that contributed to this report,
both directly, by sending in descriptions, and indirectly, by doing
all the interesting things that are reported. I hope you will find
it as interesting a read as we did.

If you haven't encountered the Haskell Communities and Activities 
Reports before, you may like to know that the first of these reports
was published in November 2001. Their goal is to improve the 
communication between the increasingly diverse groups, projects and
individuals working on, with, or inspired by Haskell. The idea behind
these reports is simple:

Every six months, a call goes out to all of you enjoying Haskell to
contribute brief summaries of your own area of work. Many of you 
respond (eagerly, unprompted, and well in time for the actual 
deadline ;) ) to the call. The editor collects all the contributions 
into a single report and feeds that back to the community.

When we try for the next update, six months from now, you might want 
to report on your own work, project, research area or group as well.
So, please put the following into your diaries now:


   End of April 2006:
target deadline for contributions to the
  May 2006 edition of the HCA Report


Unfortunately, many Haskellers working on interesting projects are so
busy with their work that they seem to have lost the time to follow
the Haskell related mailing lists and newsgroups, and have trouble even
finding time to report on their work. If you are a member, user or 
friend of a project so burdened, please find someone willing to make 
time to report and ask them to `register' with the editor for a simple 
e-mail reminder in the middle of April (you could point me to them as 
well, and we can then politely ask if they want to contribute, but it 
might work better if you do the initial asking). Of course, they will
still have to find the ten to fifteen minutes to draw up their report,
but maybe we can increase our coverage of all that is going on in the
community.

Feel free to circulate this announcement further in order to
reach people who might otherwise not see it. Enjoy!

Andres Loeh 
hcar at haskell.org

-- 
Haskell Communities and Activities Report (http://haskell.org/communities)
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[Haskell] REMINDER: Contributions to the HCA Report (November 2005 edition)

[Andres Loeh]

Dear Haskellers,

the deadline for the November 2006 edition of the Haskell Communities
and Activities Report is only a few days away -- but this is still
enough time to make sure that the report contains a section on *your*
project, on the interesting stuff that you've been doing; using or
affecting Haskell in some way.

Many projects that have been included in former reports have not yet
updated their entries. Please have a look at

  http://haskell.org/communities/topics.html

and at the May 2005 edition for reference.

* Has your project been listed in previous Reports, but is not yet
  updated? Please write a short update!

* Are you no longer working on a project that was included in the
  Report? Write up what you are working on instead, and tell me if
  someone else has picked up the project.

* Is some project you have heard about not included in any previous
  Report? Please let me know ...

There is still time to write a completely new entry, on a new
compiler, tool, library, company, user group, idea, ... -- as long as
there is a connection to the Haskell language, there is a place for it
in the Report!

Submissions are due by next Tuesday, that is

  Tuesday, 01 November 2005.

Please mail your entries to hcar at haskell dot org, in plain text
or pseudo-(La)TeX format. More information can be found in the
original Call for Contributions at

  http://www.haskell.org/pipermail/haskell/2005-October/016575.html

I look forward to receiving your contributions.

Thanks a lot,

  Andres (current editor)

-- 
Haskell Communities and Activities Report (http://haskell.org/communities)
11/2005 edition submission deadline: 01 November 2005 [EMAIL PROTECTED]
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[Haskell-cafe] REMINDER: Contributions to the HCA Report (November 2005 edition)

[Andres Loeh]

Dear Haskellers,

the deadline for the November 2006 edition of the Haskell Communities
and Activities Report is only a few days away -- but this is still
enough time to make sure that the report contains a section on *your*
project, on the interesting stuff that you've been doing; using or
affecting Haskell in some way.

Many projects that have been included in former reports have not yet
updated their entries. Please have a look at

  http://haskell.org/communities/topics.html

and at the May 2005 edition for reference.

* Has your project been listed in previous Reports, but is not yet
  updated? Please write a short update!

* Are you no longer working on a project that was included in the
  Report? Write up what you are working on instead, and tell me if
  someone else has picked up the project.

* Is some project you have heard about not included in any previous
  Report? Please let me know ...

There is still time to write a completely new entry, on a new
compiler, tool, library, company, user group, idea, ... -- as long as
there is a connection to the Haskell language, there is a place for it
in the Report!

Submissions are due by next Tuesday, that is

  Tuesday, 01 November 2005.

Please mail your entries to hcar at haskell dot org, in plain text
or pseudo-(La)TeX format. More information can be found in the
original Call for Contributions at

  http://www.haskell.org/pipermail/haskell/2005-October/016575.html

I look forward to receiving your contributions.

Thanks a lot,

  Andres (current editor)

-- 
Haskell Communities and Activities Report (http://haskell.org/communities)
11/2005 edition submission deadline: 01 November 2005 [EMAIL PROTECTED]
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Re: [Haskell] PROPOSAL: class aliases

[Andres Loeh]

 One thought: how will class aliases interact with type inference?
 e.g. if a declaration contains only a call to 'foo', should we infer
 the constraint Foo a, or FooBar a?  Can there ever be a situation where
 choosing the more specific dictionary could leave us without a 'bar'
 method at some later point in the computation?  (cf. up-casting and
 down-casting in OO languages).

 If I declare a function

 baz :: Bar a = ...

 and then pass it a value which actually has a FooBar dictionary rather
 than just a Bar, will the implementation be able to find the right
 offset in the dictionary for the 'bar' method?  How?  (I know jhc
 eliminates dictionaries at compile-time, but other implementations
 do not.)

The way I understand the proposal, there are no FooBar dictionaries
ever. John said that this can be translated by a source-to-source
translation, so internally, a FooBar dictionary *is* a Foo and a
Bar dictionary.

How much static checking can be done before desugaring the code? Will
it be possible to give sensible error messages, or will those mention
the internal classes that the alias is supposed to hide?

Cheers,
  Andres

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Re: GADT question

[Andres Loeh]

  I get an error No instance for (Fractional a) arising from the use of
  '/'  This seems odd to me, since Div is constrained to have
  fractional arguments.  Is there something obvious I'm missing?
 
 Unless GADTs are handled specially, and I don't think they are in this 
 case, this problem is not specific to GADTs but related to how
 type constraints on constructors are handled in general. Basically, a
 constraint on a constructor has no effect beyond beyond constraining 
 what the  constructor can be applied to (see the Haskell 98 report 
 4.2.1). In particular, when you take a constructed value apart through
 pattern matching, the constraints do not come into play: hence the no
 instance message.

I think this is the correct explanation. However, it might be confusing
that

   IsZ :: Num a = Term a - Term Bool

and

   eval (IsZ t) = eval t == 0

works correctly.

The difference here is that for IsZ, the compiler will store a
Num dictionary within the constructed value, because a is existentially
quantified.

On the other hand, in 

   Div :: Fractional a = Term a - Term a - Term a

the a is visible on the outside, so the compiler does not store a
dictionary. But then, while computing the pattern match

  eval (Div t u) = eval t / eval u

there's really no way to create one. So, the question is, why cannot
the compiler treat the case for Div more like the case for IsZ and store
the Fractional dictionary within the constructor?

 It has been suggested a number of times that constraints on
 constructors should have a more profound meaning, and
 maybe GADTs make this even more desirable, as your example suggest.

I think they do. Maybe the work that has already been done on
GADTs and existentials finally make it possible to give an improved
semantics to constraints on datatypes without too much additional
work.

Cheers,
  Andres
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Re: problems building ghc 6.4.1_pre using 6.4 with multiplecabalversions installed

[Andres Loeh]

 Just glancing over the patch, I can't immediately see how it works.  GHC
 6.4 gives priority to package modules over modules on the local search
 path, so Distribution.* will be taken from the installed Cabal package.
 However, when linking GHC you are ommitting -package Cabal, so I'd
 expect a link error.
 
 Hmm, I guess I should try this and figure out what's happening.

The idea is that no installed Cabal version will be used. I think the
ghc distribution should just always build its own Cabal during stage1.
That's what the patch tries to achieve, and afaics, it works. However,
Duncan didn't give you the full story with the patch. We also do the
following:

echo GHC+=-ignore-package Cabal  mk/build.mk
echo HC+=-ignore-package Cabal  mk/build.mk

This was the only way I could find to make sure that a preinstalled
Cabal is ignored whenever the preinstalled ghc is called, but not once
the in-place ghc is available.

Cheers,
  Andres
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-odir behaviour change in 6.4.1?

[Andres Loeh]

Is this change in behaviour between ghc-6.4 and ghc-6.4.1 desired:

~/trans $ ls foo
foo.c
~/trans $ ghc-6.4 -odir foo -c foo/foo.c
~/trans $ ls foo
foo.c  foo.o
~/trans $ rm foo/foo.o
~/trans $ ls foo
foo.c
~/trans $ ghc-6.4.1.20050804 -odir foo -c foo/foo.c
~/trans $ ls foo
foo  foo.c
~/trans $ ls foo/foo
foo.o

It seems to break cabal-1.1.1, in the case that I have something
like

c-sources: foo/foo.c

in my .cabal file ...

Cheers,
  Andres
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small error in building.xml

[Andres Loeh]

A recent change to the stable branch seems to have introduced a slight
error in docs/building/building.xml.

In line 3822, a /screen tag is missing.

The version that has this bug is 1.13.2.11.

Cheers,
  Andres
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[Haskell] ANNOUNCE: Haskell Communities Activities Report (8th ed., May 2005)

[Andres Loeh]

On behalf of the many, many contributors, I am pleased to announce
that the

  Haskell Communities and Activities Report
  (8th edition, May 2005)

 http://www.haskell.org/communities/

is now available from the Haskell Communities home page in several
formats: PDF, for screenreading as well as printing, HTML, for those 
of you who prefer not to deal with plugins or external viewers, and 
PostScript, for those of you who have nice quick printers that do not 
grok PDF.

Many thanks go to all the people that contributed to this report,
both directly, by sending in descriptions, and indirectly, by doing
all the interesting things that are reported. I hope you will find
it as interesting a read as we did.

If you haven't encountered the Haskell Communities and Activities 
Reports before, you may like to know that the first of these reports
was published in November 2001. Their goal is to improve the 
communication between the increasingly diverse groups, projects and
individuals working on, with, or inspired by Haskell. The idea behind
these reports is simple:

Every six months, a call goes out to all of you enjoying Haskell to
contribute brief summaries of your own area of work. Many of you 
respond (eagerly, unprompted, and well in time for the actual 
deadline ;) ) to the call. The editor collects all the contributions 
into a single report and feeds that back to the community.

When we try for the next update, six months from now, you might want 
to report on your own work, project, research area or group as well.
So, please put the following into your diaries now:


   End of October 2005:
target deadline for contributions to the
November 2005 edition of the HCA Report


Unfortunately, many Haskellers working on interesting projects are so
busy with their work that they seem to have lost the time to follow
the Haskell related mailing lists and newsgroups, and have trouble even
finding time to report on their work. If you are a member, user or 
friend of a project so burdened, please find someone willing to make 
time to report and ask them to `register' with the editor for a simple 
e-mail reminder in the middle of October (you could point us to them as 
well, and we can then politely ask if they want to contribute, but it 
might work better if you do the initial asking). Of course, they will
still have to find the ten to fifteen minutes to draw up their report,
but maybe we can increase our coverage of all that is going on in the
community.

Feel free to circulate this announcement further in order to
reach people who might otherwise not see it. Enjoy!

Andres Loeh 
hcar at haskell.org
andres at cs.uu.nl

-- 
Haskell Communities and Activities Report (http://haskell.org/communities)
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[Haskell-cafe] ANNOUNCE: Haskell Communities Activities Report (8th ed., May 2005)

[Andres Loeh]

On behalf of the many, many contributors, I am pleased to announce
that the

  Haskell Communities and Activities Report
  (8th edition, May 2005)

 http://www.haskell.org/communities/

is now available from the Haskell Communities home page in several
formats: PDF, for screenreading as well as printing, HTML, for those 
of you who prefer not to deal with plugins or external viewers, and 
PostScript, for those of you who have nice quick printers that do not 
grok PDF.

Many thanks go to all the people that contributed to this report,
both directly, by sending in descriptions, and indirectly, by doing
all the interesting things that are reported. I hope you will find
it as interesting a read as we did.

If you haven't encountered the Haskell Communities and Activities 
Reports before, you may like to know that the first of these reports
was published in November 2001. Their goal is to improve the 
communication between the increasingly diverse groups, projects and
individuals working on, with, or inspired by Haskell. The idea behind
these reports is simple:

Every six months, a call goes out to all of you enjoying Haskell to
contribute brief summaries of your own area of work. Many of you 
respond (eagerly, unprompted, and well in time for the actual 
deadline ;) ) to the call. The editor collects all the contributions 
into a single report and feeds that back to the community.

When we try for the next update, six months from now, you might want 
to report on your own work, project, research area or group as well.
So, please put the following into your diaries now:


   End of October 2005:
target deadline for contributions to the
November 2005 edition of the HCA Report


Unfortunately, many Haskellers working on interesting projects are so
busy with their work that they seem to have lost the time to follow
the Haskell related mailing lists and newsgroups, and have trouble even
finding time to report on their work. If you are a member, user or 
friend of a project so burdened, please find someone willing to make 
time to report and ask them to `register' with the editor for a simple 
e-mail reminder in the middle of October (you could point us to them as 
well, and we can then politely ask if they want to contribute, but it 
might work better if you do the initial asking). Of course, they will
still have to find the ten to fifteen minutes to draw up their report,
but maybe we can increase our coverage of all that is going on in the
community.

Feel free to circulate this announcement further in order to
reach people who might otherwise not see it. Enjoy!

Andres Loeh 
hcar at haskell.org
andres at cs.uu.nl

-- 
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Re: [Haskell-cafe] lhs2TeX and line numbers in error messages produced by LaTeX

[Andres Loeh]

 I use lhs2TeX for typesetting literate haskell code. The problem is that 
 LaTeX 
 uses the line numbers from the .tex file generated by lhs2TeX and not the 
 line number from the original .lhs file when producing error messages.
 
 Does anyone have a solution for this problem?

Sorry, I don't. I think it's very much work to change lhs2TeX so
that the generated .tex file will have the same line numbers than
the original (%include would have to be mapped to \input statements
and each code block would have to produce exactly as many lines as
the input was etc.), and AFAIK LaTeX does not have any such thing as
LINE pragmas.

I usually look at the generated file to find what LaTeX complains
about and map this to the original location mentally.
I could make lhs2TeX generate line hints as LaTeX comments, to
facilitate this process, but this would still require to read the
generated file, because the hints wouldn't be interpreted by LaTeX
automatically.

Cheers,
  Andres
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[Haskell] REMINDER: Contributions to the HCA Report (May 2005 edition)

[Andres Loeh]

Dear Haskellers,

the deadline for the May 2005 edition of the Haskell Communities and
Activities Report is only a few days away -- but this is still enough
time to make sure that the report contains a section on *your*
project, on the interesting stuff that you've been doing; using or
affecting Haskell in some way.

Many projects that have been included in former reports have not yet
updated their entries. Please have a look at

  http://haskell.org/communities/topics.html

and at the November 2004 edition for reference.

* Has your project been listed in previous Reports, but is not yet
  updated? Please write a short update!

* Are you no longer working on a project that was included in the
  Report? Write up what you are working on instead, and tell me if
  someone else has picked up the project.

* Is some project you have heard about not included in any previous
  Report? Please let me know ...

There is still time to write a completely new entry, on a new
compiler, tool, library, company, user group, idea, ... -- as long as
there is a connection to the Haskell language, there is a place for it
in the Report!

Submissions are due by next Tuesday, that is

  Tuesday, 03 May 2005.

Please mail your entries to hcar at haskell dot org, in plain text
or pseudo-(La)TeX format. More information can be found in the
original Call for Contributions at

  http://www.haskell.org/pipermail/haskell/2005-April/015688.html

I look forward to receiving your contributions.

Thanks a lot,

  Andres (current editor)

-- 
Haskell Communities and Activities Report (http://haskell.org/communities)
05/2005 edition submission deadline: 03 May 2005 [EMAIL PROTECTED]
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[Haskell-cafe] REMINDER: Contributions to the HCA Report (May 2005 edition)

[Andres Loeh]

Dear Haskellers,

the deadline for the May 2005 edition of the Haskell Communities and
Activities Report is only a few days away -- but this is still enough
time to make sure that the report contains a section on *your*
project, on the interesting stuff that you've been doing; using or
affecting Haskell in some way.

Many projects that have been included in former reports have not yet
updated their entries. Please have a look at

  http://haskell.org/communities/topics.html

and at the November 2004 edition for reference.

* Has your project been listed in previous Reports, but is not yet
  updated? Please write a short update!

* Are you no longer working on a project that was included in the
  Report? Write up what you are working on instead, and tell me if
  someone else has picked up the project.

* Is some project you have heard about not included in any previous
  Report? Please let me know ...

There is still time to write a completely new entry, on a new
compiler, tool, library, company, user group, idea, ... -- as long as
there is a connection to the Haskell language, there is a place for it
in the Report!

Submissions are due by next Tuesday, that is

  Tuesday, 03 May 2005.

Please mail your entries to hcar at haskell dot org, in plain text
or pseudo-(La)TeX format. More information can be found in the
original Call for Contributions at

  http://www.haskell.org/pipermail/haskell/2005-April/015688.html

I look forward to receiving your contributions.

Thanks a lot,

  Andres (current editor)

-- 
Haskell Communities and Activities Report (http://haskell.org/communities)
05/2005 edition submission deadline: 03 May 2005 [EMAIL PROTECTED]
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[Haskell] Call for Contributions -- HCA Report (May 2005 edition)

[Andres Loeh]

Dear Haskellers,

it is nearly time for the eighth edition of the

  
  Haskell Communities  Activities Report  
http://www.haskell.org/communities/

Submission deadline: 03 May 2005

  (please send your contributions to hcar at haskell.org, in 
plain ASCII or LaTeX format)
  

This is the short story:

* If you are working on any project that is in some way related
  to Haskell, write a short entry and submit it to the me.

* If you are interested any project related to Haskell that 
  has not previously been mentioned in the HCA Report, tell me,
  so that I can contact the project leaders and ask them to submit
  an entry.

* Feel free to pass on this call for contributions to others that
  might be interested.

More detailed information:

The Haskell Communities  Activities Report is a bi-annual overview of
the state of Haskell as well as Haskell-related projects over the
last, and possibly the upcoming 6 months. If you have only recently
been exposed to Haskell, it might be a good idea to browse the
November 2004 edition -- you will find interesting topics described as
well as several starting points and links that may provide answers to
many questions.

Contributions will be collected until the beginning of May. They will
be compiled into a coherent report which will appear sometime during
May. As always, this is a great opportunity to update your webpages,
make new releases, announce of even start new projects, or to point at
some developments you want every Haskeller to see!

As the purpose of the report is to collect recent or current
activities, we encourage you to update all existing summaries and
reports. We will probably drop any topics that have not had any
activity for the past year, i.e., since May 2004, but we would
very much prefer you to present an updated description of the
topic. Of course, new entries are more than welcome.  Reports should
generally be kept brief and informative, ranging from a few sentences
to a few hundred words, to keep the whole report reasonably sized.

Looking forward to your contributions,

Andres (current editor)

--- topics

New suggestions for current hot topics, activities, projects, etc.
are welcome - especially with names and addresses of potential
contacts, but here is a non-exclusive list of likely topics
(see also http://www.haskell.org/communities/topics.html ):

General Haskell developments; Haskell implementations; Haskell  
  extensions; Standardization and documentation; Haskell tutorials,
  howtos and wikis; Organisation of Haskell tool and library
  development; Haskell-related projects and publications; new
  research, fancy tools, long-awaited libraries, cool applications;

Feedback from specialist mailing lists to the Haskell community
  as a whole; Haskell announcements;  all (recent) things Haskell

Announcements: if you've announced anything new on the Haskell
  list over the last six months, you'll want to make sure that is
  reflected in this edition!

Project pings: if you're maintaining a Haskell tool or library or 
  somesuch, you'll want to let everyone know that it is still alive 
  and actively maintained, even if there have been no new additions,
  but all the more if there have been new developments.

Tutorials: if you've fought with some previously undocumented 
  corner of Haskell, and have been kind enough to write down how you
  did manage to build that graphical user interface, or if you've 
  written a tutorial about some useful programming techniques, 
  this is your opportunity to spread the word (short, topic-specific,  
  and hands-on tutorials that only show how to achieve a certain   
  practical task would do a lot to make things easier for new
  Haskellers - please write some!)

Applications: if you've been working quietly, using Haskell for  
  some interesting project or application (commercial or otherwise),
  you might want to let others know about what you're using Haskell
  for, and about your experiences using the existing tools and   
  libraries; are you using Haskell on your job?

  An interesting thread about using Haskell and more generally functional 
  programming for non-Haskell things seems to recur with reasonable
  frequency - why not write a sentence or two about your use of Haskell 
  for our report?

Feedback: if you're on one of the many specialist Haskell mailing
  lists, you'll want to report on whatever progress has been made 
  there (GUI API discussions, library organisation, etc.)


If you're unsure whether a contact for your area of work has come   
forward yet, have a look at the report's potential topics page, or 
get in touch with me.  I have contacted last time's contributors,  
hoping they will volunteer to provide updates of their 

[Haskell-cafe] Call for Contributions -- HCA Report (May 2005 edition)

[Andres Loeh]

Dear Haskellers,

it is nearly time for the eighth edition of the

  
  Haskell Communities  Activities Report  
http://www.haskell.org/communities/

Submission deadline: 03 May 2005

  (please send your contributions to hcar at haskell.org, in 
plain ASCII or LaTeX format)
  

This is the short story:

* If you are working on any project that is in some way related
  to Haskell, write a short entry and submit it to the me.

* If you are interested any project related to Haskell that 
  has not previously been mentioned in the HCA Report, tell me,
  so that I can contact the project leaders and ask them to submit
  an entry.

* Feel free to pass on this call for contributions to others that
  might be interested.

More detailed information:

The Haskell Communities  Activities Report is a bi-annual overview of
the state of Haskell as well as Haskell-related projects over the
last, and possibly the upcoming 6 months. If you have only recently
been exposed to Haskell, it might be a good idea to browse the
November 2004 edition -- you will find interesting topics described as
well as several starting points and links that may provide answers to
many questions.

Contributions will be collected until the beginning of May. They will
be compiled into a coherent report which will appear sometime during
May. As always, this is a great opportunity to update your webpages,
make new releases, announce of even start new projects, or to point at
some developments you want every Haskeller to see!

As the purpose of the report is to collect recent or current
activities, we encourage you to update all existing summaries and
reports. We will probably drop any topics that have not had any
activity for the past year, i.e., since May 2004, but we would
very much prefer you to present an updated description of the
topic. Of course, new entries are more than welcome.  Reports should
generally be kept brief and informative, ranging from a few sentences
to a few hundred words, to keep the whole report reasonably sized.

Looking forward to your contributions,

Andres (current editor)

--- topics

New suggestions for current hot topics, activities, projects, etc.
are welcome - especially with names and addresses of potential
contacts, but here is a non-exclusive list of likely topics
(see also http://www.haskell.org/communities/topics.html ):

General Haskell developments; Haskell implementations; Haskell  
  extensions; Standardization and documentation; Haskell tutorials,
  howtos and wikis; Organisation of Haskell tool and library
  development; Haskell-related projects and publications; new
  research, fancy tools, long-awaited libraries, cool applications;

Feedback from specialist mailing lists to the Haskell community
  as a whole; Haskell announcements;  all (recent) things Haskell

Announcements: if you've announced anything new on the Haskell
  list over the last six months, you'll want to make sure that is
  reflected in this edition!

Project pings: if you're maintaining a Haskell tool or library or 
  somesuch, you'll want to let everyone know that it is still alive 
  and actively maintained, even if there have been no new additions,
  but all the more if there have been new developments.

Tutorials: if you've fought with some previously undocumented 
  corner of Haskell, and have been kind enough to write down how you
  did manage to build that graphical user interface, or if you've 
  written a tutorial about some useful programming techniques, 
  this is your opportunity to spread the word (short, topic-specific,  
  and hands-on tutorials that only show how to achieve a certain   
  practical task would do a lot to make things easier for new
  Haskellers - please write some!)

Applications: if you've been working quietly, using Haskell for  
  some interesting project or application (commercial or otherwise),
  you might want to let others know about what you're using Haskell
  for, and about your experiences using the existing tools and   
  libraries; are you using Haskell on your job?

  An interesting thread about using Haskell and more generally functional 
  programming for non-Haskell things seems to recur with reasonable
  frequency - why not write a sentence or two about your use of Haskell 
  for our report?

Feedback: if you're on one of the many specialist Haskell mailing
  lists, you'll want to report on whatever progress has been made 
  there (GUI API discussions, library organisation, etc.)


If you're unsure whether a contact for your area of work has come   
forward yet, have a look at the report's potential topics page, or 
get in touch with me.  I have contacted last time's contributors,  
hoping they will volunteer to provide updates of their 

Re: exposed package exposes dependent packages

[Andres Loeh]

  Our example was compiling happy. happy does not import anything from
  cabal-0.5 and yet it was hit by this problem. Unless we consider 'part
  of the program' to be all modules in all exposed packages (and all
  modules in 'efectively exposed' packages like util via the cabal-0.5
  dep).
 
 You're asking GHC to decide which modules the program depends on, in
 order to figure out which packages are part of the program, rather than
 just starting from the list of exposed packages.
 
 Hmm, that might be possible... we could eagerly report module clashes in
 the exposed packages, but only report module clashes in the hidden
 packages when we know which ones are required.

This sounds like a good compromise to me. It would allow to have
some packages exposed which are not particularly well-behaved (i.e.,
pollute the name space), but you pay the price only when you're
actually using the package. 

The current situation is unfortunately very fragile. An exposed 
package that is accidentally added to the system can break the 
compilation of completely unrelated programs.

It'd be great if you could make this change in ghc.

Cheers,
  Andres
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[Haskell] ANNOUNCE: Generic Haskell 1.42 (Coral)

[Andres Loeh]

  Generic Haskell version 1.42 (Coral)
  

We are happy to announce the third release of Generic Haskell,
an extension of Haskell that facilitates generic programming.

Generic Haskell includes the following features:

* type-indexed values -- generic functions that can be
  instantiated on all Haskell data types.

* type-indexed types -- types which are indexed over the type
  constructors underlying Haskell datatypes.

The Generic Haskell compiler takes Generic Haskell source
and produces Haskell code.

Changes since 1.23 (Beryl)
--

* Dependency-style Generic Haskell [1] is supported, i.e.,
  generic functions can be written in a simpler and more
  natural style. In particular, type signatures of generic
  functions have become simpler -- there is no need to define
  kind-indexed types any longer.

* Local redefinition, generic abstraction, and default cases
  are now implemented as described in 
  Exploring Generic Haskell [2].

Download


The Generic Haskell compiler is available in source and binary
distributions. Binaries for Linux, Windows, and MacOSX
are available. These are available from:

http://www.generic-haskell.org/compiler.html

The documentation is also available separately from that page.

For more general information, point your browser to:

http://www.generic-haskell.org


Why Generic Haskell?


Software development often consists of designing datatypes, around
which functionality is added.  Some functionality is datatype
specific, whereas other functionality is defined on almost all
datatypes in such a way that it depends only on the structure of the
datatype.  A function that works on many datatypes in this way
is called a generic function.  Examples of generic functionality 
include editing, pretty-printing or storing a value in a database, 
and comparing two values for equality.

Since datatypes often change and new datatypes are introduced, we 
have developed Generic Haskell, an extension of the functional 
programming language Haskell that supports generic definitions, 
to save the programmer from (re)writing instances of generic 
functions. The original design of Generic Haskell is based on work 
by Ralf Hinze.


  Pleasant programming,
  The Generic Haskell Team at Utrecht University

  [EMAIL PROTECTED]



[1] A. Loeh, D. Clarke, and J. Jeuring. Dependency-style Generic Haskell. 
In O. Shivers, editor, Proceedings of the International Conference on 
Functional Programming, ICFP'03, pages 141--152. ACM Press, August 2003. 

[2] A. Loeh. Exploring Generic Haskell. PhD thesis, Utrecht University,
September 2004.
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Re: [Haskell-cafe] The difference between ($) and application

[Andres Loeh]

 Date: Tue, 14 Dec 2004 10:24:15 -0500
 From: Andrew Pimlott [EMAIL PROTECTED]
 Subject: Re: [Haskell-cafe] The difference between ($) and application
 
 On Tue, Dec 14, 2004 at 11:23:24AM +0100, Henning Thielemann wrote:
  
  On Tue, 14 Dec 2004, Andrew Pimlott wrote:
  
   (Of course, it's still useful, by itself or in a slice, as a higher-order
   operator.)
  
  You can also use 'id' in this cases, right?
 
 I'm thinking of things like
 
 zipWith ($)
 map ($ x)

You can indeed use

zipWith id
map (`id` x)

instead. Look at the types:

id  :: a -  a
($) :: (a - b)  -  (a - b)

The function ($) is the identity function, 
restricted to functions.

Nevertheless, I find using ($) in such a situation 
more descriptive than using id.

Cheers,
  Andres
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[Haskell] ANNOUNCE: Haskell Communities Activities Report (7th ed., November 2004)

[Andres Loeh]

Right in time, I am pleased to announce -- on behalf of the many
contributers -- that the

  Haskell Communities and Activities Report
  (7th edition, November 2004)

 http://www.haskell.org/communities/

is now available from the Haskell Communities home page in several
formats: PDF, for screenreading as well as printing, HTML, for those 
of you who prefer not to deal with plugins or external viewers, and 
PostScript, for those of you who have nice quick printers that do not 
grok PDF.

Many thanks go to all the people that contributed to this report,
both directly, by sending in descriptions, and indirectly, by doing
all the interesting things that are reported. I hope you will find
it as interesting a read as we did.

If you haven't encountered the Haskell Communities and Activities 
Reports before, you may like to know that the first of these reports
was published in November 2001. Their goal is to improve the 
communication between the increasingly diverse groups, projects and
individuals working on, with, or inspired by Haskell. The idea behind
these reports is simple:

Every six months, a call goes out to all of you enjoying Haskell to
contribute brief summaries of your own area of work. Many of you 
respond (eagerly, unprompted, and well in time for the actual 
deadline ;) ) to the call. The editor collects all the contributions 
into a single report and feeds that back to the community.

When we try for the next update, six months from now, you might want 
to report on your own work, project, research area or group as well.
So, please put the following into your diaries now:


   End of April 2005:
target deadline for contributions to the
  May 2005 edition of the HCA Report


Unfortunately, many Haskellers working on interesting projects are so
busy with their work that they seem to have lost the time to follow
the Haskell related mailing lists and newsgroups, and have trouble even
finding time to report on their work. If you are a member, user or 
friend of a project so burdened, please find someone willing to make 
time to report and ask them to `register' with the editor for a simple 
e-mail reminder in the middle of April (you could point us to them as 
well, and we can then politely ask if they want to contribute, but it 
might work better if you do the initial asking). Of course, they will
still have to find the ten to fifteen minutes to draw up their report,
but maybe we can increase our coverage of all that is going on in the
community.

Feel free to circulate this announcement further in order to
reach people who might otherwise not see it. Enjoy!

Andres Loeh 
[EMAIL PROTECTED]
[EMAIL PROTECTED]


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[Haskell-cafe] ANNOUNCE: Haskell Communities Activities Report (7th ed., November 2004)

[Andres Loeh]

Right in time, I am pleased to announce -- on behalf of the many
contributers -- that the

  Haskell Communities and Activities Report
  (7th edition, November 2004)

 http://www.haskell.org/communities/

is now available from the Haskell Communities home page in several
formats: PDF, for screenreading as well as printing, HTML, for those 
of you who prefer not to deal with plugins or external viewers, and 
PostScript, for those of you who have nice quick printers that do not 
grok PDF.

Many thanks go to all the people that contributed to this report,
both directly, by sending in descriptions, and indirectly, by doing
all the interesting things that are reported. I hope you will find
it as interesting a read as we did.

If you haven't encountered the Haskell Communities and Activities 
Reports before, you may like to know that the first of these reports
was published in November 2001. Their goal is to improve the 
communication between the increasingly diverse groups, projects and
individuals working on, with, or inspired by Haskell. The idea behind
these reports is simple:

Every six months, a call goes out to all of you enjoying Haskell to
contribute brief summaries of your own area of work. Many of you 
respond (eagerly, unprompted, and well in time for the actual 
deadline ;) ) to the call. The editor collects all the contributions 
into a single report and feeds that back to the community.

When we try for the next update, six months from now, you might want 
to report on your own work, project, research area or group as well.
So, please put the following into your diaries now:


   End of April 2005:
target deadline for contributions to the
  May 2005 edition of the HCA Report


Unfortunately, many Haskellers working on interesting projects are so
busy with their work that they seem to have lost the time to follow
the Haskell related mailing lists and newsgroups, and have trouble even
finding time to report on their work. If you are a member, user or 
friend of a project so burdened, please find someone willing to make 
time to report and ask them to `register' with the editor for a simple 
e-mail reminder in the middle of April (you could point us to them as 
well, and we can then politely ask if they want to contribute, but it 
might work better if you do the initial asking). Of course, they will
still have to find the ten to fifteen minutes to draw up their report,
but maybe we can increase our coverage of all that is going on in the
community.

Feel free to circulate this announcement further in order to
reach people who might otherwise not see it. Enjoy!

Andres Loeh 
[EMAIL PROTECTED]
[EMAIL PROTECTED]


-- 
Haskell Communities and Activities Report (http://haskell.org/communities)

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Re: typechecking too eager?

[Andres Loeh]

Hi there,

 The following code should compile (If the constructor
 is valid, so is the function):
 
 data Test = Test (forall a . a)
 test a = Test a
 
 However this fails to compile with the following error:

The current implementation of rank-n polymorphism
(which is documented in the paper Pratical type inference
for arbitrary-rank types) does not guess polymorphic
types for lambda-abstracted values.

In this situation, this means that the variable a
is assumed to have a monorphic type, which then cannot
be passed to Test as an argument.

Knowledge about polymorphism is passed down/inwards,
but not up/outwards.

This definition typechecks only if you add a type
signature:

test :: (forall a . a) - Test

If you want to know the reasons, read the paper. It explains
the problems very well.

Cheers,
  Andres

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[Haskell] REMINDER: Contributions to the HCA Report (November 2004 edition)

[Andres Loeh]

Dear Haskellers,

the deadline for the November 2004 edition of the
Haskell Communities and Activities is approaching
quickly -- but there are still a few days left to make 
sure that the report contains a section on *your* 
project, on the interesting stuff that you've been 
doing, using or affecting Haskell in some way.

In particular, any information regarding upcoming, 
Haskell-related, events is highly appreciated 
(conferences, workshops, summer schools ...).

Many FP research groups have not yet updated their
reports.

Furthermore, please have a look at 

  http://haskell.org/topics.html

* Is your project listed, but not yet updated? Please
  write a short update!

* Is a project listed that you are no longer working on?
  Write up what you are working on instead, and tell me
  if someone else has picked up the project.

* Is something you have heard about not in the list? 
  Please let me know ...

There is still time to write a completely new entry,
on a new compiler, tool, library, company, user group,
idea, ... -- as long as there is a connection to the
Haskell language, there is a place for it in the
report!

Submissions are due by the end of this week, that is

  Friday, 29 October 2004.

Please mail your entries to hcar at haskell dot org, 
in plain text or pseudo-(La)TeX format.

I look forward to receiving your contributions.

Thanks a lot,

  Andres (current editor)

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[Haskell] Re: REMINDER: Contributions to the HCA Report (November 2004 edition)

[Andres Loeh]

Sorry, the link was incorrect. The pointer
should have been:

 Furthermore, please have a look at 
 

http://haskell.org/communities/topics.html

Cheers,
  Andres

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[Haskell-cafe] REMINDER: Contributions to the HCA Report (November 2004 edition)

[Andres Loeh]

Dear Haskellers,

the deadline for the November 2004 edition of the
Haskell Communities and Activities is approaching
quickly -- but there are still a few days left to make 
sure that the report contains a section on *your* 
project, on the interesting stuff that you've been 
doing, using or affecting Haskell in some way.

In particular, any information regarding upcoming, 
Haskell-related, events is highly appreciated 
(conferences, workshops, summer schools ...).

Many FP research groups have not yet updated their
reports.

Furthermore, please have a look at 

  http://haskell.org/topics.html

* Is your project listed, but not yet updated? Please
  write a short update!

* Is a project listed that you are no longer working on?
  Write up what you are working on instead, and tell me
  if someone else has picked up the project.

* Is something you have heard about not in the list? 
  Please let me know ...

There is still time to write a completely new entry,
on a new compiler, tool, library, company, user group,
idea, ... -- as long as there is a connection to the
Haskell language, there is a place for it in the
report!

Submissions are due by the end of this week, that is

  Friday, 29 October 2004.

Please mail your entries to hcar at haskell dot org, 
in plain text or pseudo-(La)TeX format.

I look forward to receiving your contributions.

Thanks a lot,

  Andres (current editor)

-- 
Haskell Communities and Activities Report (http://haskell.org/communities)
11/2004 edition submission deadline: 29 October 2004 [EMAIL PROTECTED]
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[Haskell-cafe] Re: REMINDER: Contributions to the HCA Report (November 2004 edition)

[Andres Loeh]

Sorry, the link was incorrect. The pointer
should have been:

 Furthermore, please have a look at 
 

http://haskell.org/communities/topics.html

Cheers,
  Andres

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Re: deriving...

[Andres Loeh]

 | Why not even simply
 | 
 | instance Typeable (T a)
 | 
 | In other words, derivable classes define default
 | implementations for all their methods.
 
 But that has an existing meaning!  It means use the default methods for
 all methods of the class.  Which is not the same as derive all
 methods.

I was thinking about the proposed syntax in the
Derivable Type Classes paper, which was just
this.

In classic Haskell, I can see that it is problematic
whenever default methods are specified in terms of each other,
like (==) and (/=) in Eq.

I would then vote for

 It'd have to be
   instance Typeable (T a) deriving

Perhaps it would be not much harder to allow

instance Show MyChar deriving where
  showList = ...

to partially override derived functions as well.

 The trouble is, as you mention, that instance decls usually have a
 context.  I'd be quite happy to require a context in these derived
 instances too, so you have to write
   derive instance Typeable a = Typeable (T a)
 Then it looks more like a regular instance decl.

Yes, even though it's more to write, I think it's cleaner
if the context is specified. After all, the old deriving
syntax within the data declaration will continue to be
available for compatibility.

Cheers,
  Andres
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Re: deriving...

[Andres Loeh]

 Simon Peyton-Jones wrote:
   derive( Typeable (T a) )
 
 But that means adding 'derive' as a keyword.  Other possibilities:
   
   deriving( Typeable (T a) )
  -- (B) Re-use 'deriving' keyword
 
 The trouble with (B) is that the thing inside the parens is different in 
 this situation than in a data type declaration. 
 Any other ideas?
 
   instance Typeable (T a) deriving

Why not even simply

instance Typeable (T a)

In other words, derivable classes define default
implementations for all their methods.

Advantages:
  (1) no syntax change at all required
  (2) derived class instances can be partially
  redefined by the user

Disadvantages:
  (1) Slightly more work in some cases because
  a complete instance declaration is required.
  Example:

  instance Eq a = Eq (T a)


Cheers,
  Andres
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[Haskell] Call for Contributions -- HCA Report (November 2004 edition)

[Andres Loeh]

Dear Haskellers,

another six months have passed, and another change of editor has
occurred. Half a year usually also is plenty of time for several
productive changes and news to occur within the Haskell community,
and therefore it is time for you to start writing: please
contribute to the forthcoming seventh edition of the

  
  Haskell Communities  Activities Report  
http://www.haskell.org/communities/

Submission deadline: 29 October 2004

  (please send your contributions to [EMAIL PROTECTED], in 
plain ASCII or LaTeX format)
  

The Haskell Communities  Activities Report is a bi-annual overview
of the state of Haskell as well as Haskell-related projects over
the last, and possibly the upcoming 6 months. If you have only
recently been exposed to Haskell, it might be a good idea to browse
the May 2004 edition -- you will find interesting topics
described as well as several starting points and links that may
provide answers to many questions.

The plan is to collect contributions until roughly the end of
October, then start to compile them into a coherent report which
will appear during November. As always, this is a great opportunity
to update your webpages, make new releases, announce of even start
new projects, or to point at some developments you want every
Haskeller to see!

As the purpose of the report is to collect recent or current
activities, we encourage you to update all existing summaries
and reports. We will drop any topics that have not had any
activity for the past year, i.e., since November 2003, but we
would very much prefer you to present an updated description
of the topic. Of course, new entries are more than welcome.
Reports should generally be kept brief and informative, ranging 
from a few sentences to a few hundred words, to keep the whole
report reasonably sized.

Looking forward to your contributions,

Andres (current editor)

--- topics

New suggestions for current hot topics, activities, projects, etc.
are welcome - especially with names and addresses of potential
contacts, but here is a non-exclusive list of likely topics
(see also http://www.haskell.org/communities/topics.html ):

General Haskell developments; Haskell implementations; Haskell  
  extensions; Standardization and documentation; Haskell tutorials,
  howtos and wikis; Organisation of Haskell tool and library
  development; Haskell-related projects and publications; new
  research, fancy tools, long-awaited libraries, cool applications;

Feedback from specialist mailing lists to the Haskell community
  as a whole; Haskell announcements;  all (recent) things Haskell

Announcements: if you've announced anything new on the Haskell
  list over the last six months, you'll want to make sure that is
  reflected in this edition!

Project pings: if you're maintaining a Haskell tool or library or 
  somesuch, you'll want to let everyone know that it is still alive 
  and actively maintained, even if there have been no new additions,
  but all the more if there have been new developments.

Tutorials: if you've fought with some previously undocumented 
  corner of Haskell, and have been kind enough to write down how you
  did manage to build that graphical user interface, or if you've 
  written a tutorial about some useful programming techniques, 
  this is your opportunity to spread the word (short, topic-specific,  
  and hands-on tutorials that only show how to achieve a certain   
  practical task would do a lot to make things easier for new
  Haskellers - please write some!)

Applications: if you've been working quietly, using Haskell for  
  some interesting project or application (commercial or otherwise),
  you might want to let others know about what you're using Haskell
  for, and about your experiences using the existing tools and   
  libraries; are you using Haskell on your job?

  An interesting thread about using Haskell and more generally functional 
  programming for non-Haskell things seems to recur with reasonable
  frequency - why not write a sentence or two about your use of Haskell 
  for our report?

Feedback: if you're on one of the many specialist Haskell mailing
  lists, you'll want to report on whatever progress has been made 
  there (GUI API discussions, library organisation, etc.)


If you're unsure whether a contact for your area of work has come   
forward yet, have a look at the report's potential topics page, or 
get in touch with me.  I have contacted last time's contributors,  
hoping they will volunteer to provide updates of their reports, and
will update the contacts on the topics page fairly regularly.  But 
where you don't yet see contacts listed for your own subject of
interest, you are very welcome to volunteer, or to remind 

Re: HOpenGL buglet

[Andres Loeh]

Sven's fix that Simon M. mentioned will appear in 6.2.2 is included in
the Gentoo ebuild ghc-6.2.1-r1.ebuild .

If it still doesn't work with that version, please report it as a
Gentoo bug on bugs.gentoo.org.

Cheers,
  Andres

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Re: [wxhaskell-users] RE: [Haskell] Dynamically loading wxhaskell?

[Andres Loeh]

 That is probably the problem. I did not see all messages of this thread,
 but one should indeed use --with-opengl on wxHaskell configure if 
 wxWidgets
 was build with --with-opengl.
 
 Unfortunately, due to wxWidgets changes, I can not automatically detect the
 need for this flag, but I promise to discuss it with the wxWidgets
 devs.

I think this has been discussed before: as far as I can see, the flag
--with-opengl is always safe, and should therefore be the default.
The call to wx-config --gl-libs returns the empty string if
wxWidgets has not been built using GL.

Best,
  Andres
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Re: [Haskell] Parsing Typed Data from a String

[Andres Loeh]

 So my question is, is there any method in GHC which allows you to
 extract the order of the constructors in a type or to parse a
 type-representation in such a way that the order of the records doesn't
 matter (I am looking for ease/simplicity of use)?

If you happen to use Parsec for parsing -- it has permutation
parser combinators in Text.ParserCombinators.Parsec.Perm.

So has the UUST parser combinator library, in UU.Parsing.Perms.

Best,
  Andres
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Re: Getting lhs2tex working under Win32 (was Re: ANNOUNCE: lhs2tex-1.9)

[Andres Loeh]

 Thanks for producing such a wonderful and useful tool!

Nice to hear that you find it useful. Thank you very much for sharing
your results.

 I am pleased to report that I managed to get lhs2TeX working on Win32, 
 by modifying just a single byte in the source code.  

 1.  In the lhs2TeX sources, change line 42 of FileNameUtils.lhs from:
environmentSeparators =  ;:
 to:
environmentSeparators =  ;
 and do another make install.

Yes, that's a good fix for Windows. Actually, I copied this code
from Generic-Haskell, and simplified it because I only needed it for
Unix and did not have time to test it under Windows anyway.

For the next release, I will try to merge the full Generic-Haskell
library, which defines environmentSeparators and a few other
functions in several OSSpecific.hs files, one of which can,
depending on architecture, be included by lhs2TeX.

 Instead, I propose that it would be very valuable if there were some 
 standardized, portable library that Haskell programs like lhs2TeX could 
 use for locating files that should be installed with the program.
[...]

I agree on all that. I even think that there probably are several
projects that have done most of that already, and that it would just
be necessary to collect some source code and streamline the interface.
I like the Python interface, BTW. It seems simple and pragmatic
enough.

Thanks again.

Andres

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ANNOUNCE: lhs2tex-1.9

[Andres Loeh]

 lhs2TeX version 1.9
 ===

We are pleased to announce the first official release of
lhs2TeX, a preprocessor to generate LaTeX code from literate
Haskell sources.

lhs2TeX includes the following features:

* Different styles to process your source file: for instance,
  tt style uses a monospaced font for the code while still 
  allowing you to highlight keywords etc, whereas
  poly style uses proportional fonts for identifiers, handles
  indentation nicely, is able to replace binary operators by
  mathematical symbols and take care of complex horizontal
  alignments.

* Formatting directives, which let you customize the way certain
  tokens in the source code should appear in the processed 
  output.

* A liberal parser that can handle most of the language 
  extensions; you don't have to restrict yourself to Haskell 98.

* Preprocessor-style conditionals that allow you to generate
  different versions of a document from a single source file
  (for instance, a paper and a presentation).

* Active documents: you can use Haskell to generate parts of the 
  document (useful for papers on Haskell).

* A manual explaining all the important aspects of lhs2TeX.

Changes
---

Although development on lhs2TeX has begun as early as 1997,
it has never been formally released before. This is a first
release that should be mostly compatible to versions that
have been inofficially distributed so far. It should compile
with the latest GHC versions.

Two completely new modes have been added compared to previous
versions: poly mode is designed to replace the old math
mode; the restriction of having only one alignment column 
per code block is lifted and replaced by a generic mechanism
that allows complex layouts; newcode is a replacement for
the old code mode that can handle formatting directives
and produces LINE pragmas in the generated code.

Requirements and Download
-

A source distribution that should be suitable for Unix-based
environments is available from

  http://www.cs.uu.nl/~andres/lhs2tex/

It has been verified to build on Linux and MacOSX.

You need a recent version of GHC (5.04.X or higher should do) 
to build lhs2TeX, and, of course, you need a TeX distribution 
to make use of lhs2TeX's output. The program includes a 
configuration that is suitable for use with LaTeX. In theory, 
there should be no problem to generate code for other TeX 
flavors, such as plainTeX or ConTeXt.


  Happy lhs2TeXing,
  Ralf Hinze and Andres Loeh

  [EMAIL PROTECTED]
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Re: ANNOUNCE: lhs2tex-1.9

[Andres Loeh]

  In theory, there should be no problem to generate code for other TeX flavors,
  such as plainTeX or ConTeXt.
 
 Any plan to maybe add support for ConteXt?

Not now. Maybe in half a year or so. I am using ConTeXt for some
things, so sooner or later it would be nice to support it. If you
don't want poly style (i.e. only math), it's only the matter of
writing some directives which is not hard -- I think I even have
an experimental .fmt file lying around somewhere.
But poly style depends on polytable.sty, and this package has to be
translated into a ConTeXt module, which should be possible, but would
take more time, unfortunately, than I have right now. Sorry.

Of course, you're welcome to try yourself. Patches are welcome.

Best,
  Andres
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