Re: [Haskell-cafe] hackage feature request: revision control location

[Henning Thielemann]

On Fri, 24 Oct 2008, zooko wrote:


Hi folks:

I'm trying to use hackage/cabal/cabal-install, and I have a feature request: 
it would be nice if the metadata about the package, which is displayed on 
e.g. "hackage-scripts/package/HTTP" had a field for the revision control tool 
that is used on that package (if any) and the publicly-readable repository 
for that package (if any).


I also like this feature.

http://hackage.haskell.org/trac/hackage/ticket/58
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[Haskell-cafe] Re: [Haskell] ANNOUNCE: colour 0.0.0

[roconnor]

On Fri, 24 Oct 2008, Henk-Jan van Tuyl wrote:

I think it would be nice to have conversion functions for wxHaskell and the 
like, to convert between the different color representations.


I agree; however, it will be upto the wxHaskell (and gtk2hs, etc) people 
to import this library and implement this.


--
Russell O'Connor  
``All talk about `theft,''' the general counsel of the American Graphophone
Company wrote, ``is the merest claptrap, for there exists no property in
ideas musical, literary or artistic, except as defined by statute.''
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[Haskell-cafe] Re: [Haskell] ANNOUNCE: colour 0.0.0

[roconnor]

On Fri, 24 Oct 2008, Sebastian Sylvan wrote:


Another useful predefined space which I didn't see is the YCoCg space, which is 
used in lots of
compression schemes (like H.264 IIRC).


YCoCg, like HLS and HSV, seems to not really be a colour space because it 
isn't well specified.  A transformation is given from some unknown RGB 
space.


Perhaps I should make a datatype for unknown RGB triple, and create HLS 
HSV, and YCoCg transforms from this type.  I can have toRGB709 and toSRGB 
take and return this unknown RGB triple type.


This would suggest changing sRGB and rgb709 from the type
sRGB :: a -> a -> a -> Colour a

to

sRGB :: RGB a -> Colour a

so the code "sRGB r g b" becomes "sRGB (RGB r g b)".  That doesn't seem 
very nice.


Also, I could add phantom type annotations to the RGB triple type, 
allowing it to be labeled as linear, or nonlinear, or other information.


--
Russell O'Connor  
``All talk about `theft,''' the general counsel of the American Graphophone
Company wrote, ``is the merest claptrap, for there exists no property in
ideas musical, literary or artistic, except as defined by statute.''
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[Haskell-cafe] ANN: Lambdabot 4.2.2

[Gwern Branwen]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA512

A quick note. Today was released the 4.2.2 version of the IRC bot
Lambdabot. You can find it at
,
and the usual Darcs repository .

What is interesting about this release?

* Less buggy. A few UTF-related bugs were fixed, some formatting bugs, etc.
* Updated state (ever more @quote goodness)
* New feature: Lambdabot can now be run in arbitrary directories like
~/. Before, one *had* to run in the darcs-gotten directory - Lambdabot
had all sorts of hardwired constants like "./State/quotes" in it. Now
the situation is such: Lambdabot first looks for a ./State/ and so on;
if it finds a populated State/, it will read and write those files
just like an old Lambdabot would. However, if State/ is not there,
then Lambdabot will  look for ~/.lambdabot/, and use the State/
hierarchy inside it, just as normal. Should there be neither a local
directory, nor a ~/ directory, then Lambdabot will ask Cabal where all
its State files were stuffed (presumably in /usr/share or wherever),
and copy them to ~/.lambdabot, and try the sequence again. The upshot
is that now you can be in ~/ or ~/bin/xmonad or anywhere, and type
'lambdabot' for a quick session.
* No more dependency on BotPP and crazy pre-build processing, thanks
to some Template Haskell contributed by sjanssen
* those changes included in this classification
* innumerable ones;
* those drawn with a very fine camel's-hair brush;
* etcetera
* just broken the flower vase;
* those that at a distance resemble flies

- --
gwern
-BEGIN PGP SIGNATURE-
Version: GnuPG v1.4.9 (GNU/Linux)
Comment: http://getfiregpg.org

iEYEAREKAAYFAkkCfX4ACgkQvpDo5Pfl1oK/kQCeJAqdv4yNerXrhBQKaHjQlXWJ
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[Haskell-cafe] ANN: Autoproc Change of Maintainer (if you use procmail you should read this)

[Jason Dagit]

What is autoproc?
-
Tired writing procmail recipes by hand?

You're in luck!

Autoproc makes it quick and easy for Haskell programmers to make
procmail recipes by using an embedded domain specific language.  Once
your recipes type check and compile you simply run autoproc and it
generates the corresponding procmail recipe on your screen.  If you
like the results, store it in ~/.procmailrc and enjoy!

What's with this announcement?
---
I created autoproc a few years ago, but in that time I've farmed out
my email to gmail and I'm no longer using procmail.  In the meantime,
Gwern Branwen has contributed nice features to the project to make it
friendlier to use, cabalization and so on.  With his permission, I am
now declaring him the official maintainer and dictator for life.  Long
live Autoproc!  Long live Gwern Branwen!

Find it on Hackage:
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/autoproc

Find it on code.haskell.org:
darcs get http://code.haskell.org/autoproc

Note: We're using a darcs2 format repository, so to get the
development version you'll need darcs 2.0 or newer.


Thanks and enjoy your day!
Jason
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Re: [Haskell-cafe] Crash!

[Derek Elkins]

On Fri, 2008-10-24 at 17:16 -0400, John Dorsey wrote:
> Quoth Tim Newsham:
> > >Haskell programs with particular constraints (i.e. pure, total Haskell, 
> > >doesn't
> > >primarily call gtk...)
> > 
> > Yup, and that's a great thing that we should be evangelizing to
> > all potential users.  No need to go overboard and tell them that
> > there will never be a crash, though..  The robustness claim is
> > strong enough without embellishment.
> 
> Pure, total Haskell programs may blow the stack.
> 

Total is unnecessary (with regards to the earlier comment, not the
immediately preceding one.)

> Just what is the concise, compelling, unembellished claim regarding
> Haskell's inherent robustness?

The concise, compelling, unembellished claim is: if your "pure*" Haskell
program segfaults (or GPFs) then it's the implementation's fault, not
yours. [unless your OS/Arch is stupid]

This isn't unique to Haskell, every memory-safe language has it.

* "pure" as in "100% pure Java" which has similar claims


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Re: [Haskell-cafe] Crash!

[Derek Elkins]

On Fri, 2008-10-24 at 19:22 +0100, Andrew Coppin wrote:
> Tim Newsham wrote:
> >> The point is... I'm not doing that. Gtk2hs is, but that's a 
> >> well-tested library, so I very much doubt it's the source of the bug.
> >
> > I don't understand why Haskell users believe (perhaps are too often 
> > led to believe) that haskell programs can't crash.  Gtk2hs does a lot 
> > of native stuff.  Gtk's been around for a long time, but so has a lot 
> > of other software that has lots of bugs still present in it. Often 
> > these bugs lead to memory corruption and crashes.  Haskell does 
> > nothing to prevent this from happening (how could it?).
> >
> > I entirely expect that this crash is due to Gtk2hs (well-tested though 
> > it may be) or one of its underlying dependencies (such as libpng).
> 
> Nope. Actually it was me being dumb with unchecked array access. Nothing 
> wrong with GHC, GTK+ or even Gtk2hs.

I, for one, am completely unsurprised.  Haskell doesn't make you smarter
than you are when programming in C.  If you are using unsafe functions
you have a very significant burden of proof to acquire before you can
say it is the compiler or run-time or a mature library, though there are
certainly bugs in all of those.

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Re: [Haskell-cafe] Crash!

[John Dorsey]

Quoth Tim Newsham:
> >Haskell programs with particular constraints (i.e. pure, total Haskell, 
> >doesn't
> >primarily call gtk...)
> 
> Yup, and that's a great thing that we should be evangelizing to
> all potential users.  No need to go overboard and tell them that
> there will never be a crash, though..  The robustness claim is
> strong enough without embellishment.

Pure, total Haskell programs may blow the stack.

Just what is the concise, compelling, unembellished claim regarding
Haskell's inherent robustness?

Regards,
John Dorsey

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Re: [Haskell-cafe] The Haskell type inference feature I'd really like to see

[John Meacham]

On Fri, Oct 24, 2008 at 01:38:23PM -0700, Dan Piponi wrote:
> I'd like to be able to write something like
> 
> > map zipWith ([1,2,3] >>= printMyInferredType)
> 
> and have the compiler treat 'printMyInferredType' as undefined, but
> also produce the side effect of printing out its inferred type.
> 
> What's the easiest way to simulate this with what we have now?

This will work as long as your type has a typeable instance. You can
modify it to work in an non-io context with unsafePerformIO (as long as
you are aware of the caveats of doing so)



import Data.Typeable

printInferedType :: Typeable a => a -> IO ()
printInferedType x = print (typeOf x)


main = do
printInferedType ()
printInferedType "foo"

-- 
John Meacham - ⑆repetae.net⑆john⑈
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[Haskell-cafe] The Haskell type inference feature I'd really like to see

[Dan Piponi]

I'd like to be able to write something like

> map zipWith ([1,2,3] >>= printMyInferredType)

and have the compiler treat 'printMyInferredType' as undefined, but
also produce the side effect of printing out its inferred type.

What's the easiest way to simulate this with what we have now?
--
Dan
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Re: [Haskell-cafe] Crash!

[Tim Newsham]

Haskell programs with particular constraints (i.e. pure, total Haskell, doesn't
primarily call gtk...)


Yup, and that's a great thing that we should be evangelizing to
all potential users.  No need to go overboard and tell them that
there will never be a crash, though..  The robustness claim is
strong enough without embellishment.


-- Don


Tim Newsham
http://www.thenewsh.com/~newsham/
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[Haskell-cafe] hackage feature request: revision control location

[zooko]

Hi folks:

I'm trying to use hackage/cabal/cabal-install, and I have a feature  
request: it would be nice if the metadata about the package, which is  
displayed on e.g. "hackage-scripts/package/HTTP" had a field for the  
revision control tool that is used on that package (if any) and the  
publicly-readable repository for that package (if any).


Thanks!

Regards,

Zooko
---
http://allmydata.org -- Tahoe, the Least-Authority Filesystem
http://allmydata.com -- back up all your files for $10/month
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Re: [Haskell-cafe] Crash!

[Andrew Coppin]

Tim Newsham wrote:
The point is... I'm not doing that. Gtk2hs is, but that's a 
well-tested library, so I very much doubt it's the source of the bug.


I don't understand why Haskell users believe (perhaps are too often 
led to believe) that haskell programs can't crash.  Gtk2hs does a lot 
of native stuff.  Gtk's been around for a long time, but so has a lot 
of other software that has lots of bugs still present in it. Often 
these bugs lead to memory corruption and crashes.  Haskell does 
nothing to prevent this from happening (how could it?).


I entirely expect that this crash is due to Gtk2hs (well-tested though 
it may be) or one of its underlying dependencies (such as libpng).


Nope. Actually it was me being dumb with unchecked array access. Nothing 
wrong with GHC, GTK+ or even Gtk2hs.


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[Haskell-cafe] Fixed: Crash!

[Andrew Coppin]

Andrew Coppin wrote:
I'm actually wondering if my code is writing off the end of an array 
and this "just happens" to hit some data structure used by GTK+? (In 
which case, minute changes in linkage, etc., would disturb the bug.)


Yep, that's what it was. (Although not where I was expecting it to be, 
which kept me guessing for a while...) I thought that all write 
operations go to the IOUArray, except for the loop that copies it to the 
Pixbuf. (This loop is constructed such that it cannot go out of bounds, 
while the ad-hoc writing uses user-supplied coordinates.) I forgot about 
the second drawing pass, which does write directly to the Pixbuf. *This* 
appears to be the source of my bug; if you add a range check, the bug 
goes away. (Oddly, I added the range check back to the IOUArray as well, 
and even though it's writing the same coordinates, no error is reported. 
I guess I must have an off-by-one bug as well...!)


So there you have it. Premature optimisation => buffer overrun => end of 
civilisation as we know it. :-/


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Re: [Haskell-cafe] Crash!

[Andrew Coppin]

Bulat Ziganshin wrote:

Hello Andrew,

Thursday, October 23, 2008, 11:42:04 PM, you wrote:

  

Theoretically, feeding invalid coordinates to the program might make it
run off the end of the IOUArray (or maybe off the beginning of it), but
I don't see what that has to do with GTK+...



replace unsafe writes with simple ones and try again
  


It would be *so much* nicer if both of them had the same type 
signature... (But I won't hold my breath for that change to happen!)


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Re: [Haskell-cafe] Crash!

[Don Stewart]

newsham:
> >The point is... I'm not doing that. Gtk2hs is, but that's a well-tested 
> >library, so I very much doubt it's the source of the bug.
> 
> I don't understand why Haskell users believe (perhaps are too often led to 
> believe) that haskell programs can't crash.  Gtk2hs does a lot of native 
> stuff.  Gtk's been around for a long time, but so has a lot of other 
> software that has lots of bugs still present in it. Often these bugs lead 
> to memory corruption and crashes.  Haskell does nothing to prevent this 
> from happening (how could it?).

Haskell programs with particular constraints (i.e. pure, total Haskell, doesn't
primarily call gtk...)

-- Don
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Re: [Haskell-cafe] Crash!

[Tim Newsham]

The point is... I'm not doing that. Gtk2hs is, but that's a well-tested 
library, so I very much doubt it's the source of the bug.


I don't understand why Haskell users believe (perhaps are too often led to 
believe) that haskell programs can't crash.  Gtk2hs does a lot of native 
stuff.  Gtk's been around for a long time, but so has a lot of other 
software that has lots of bugs still present in it. Often these bugs lead 
to memory corruption and crashes.  Haskell does nothing to prevent this 
from happening (how could it?).


I entirely expect that this crash is due to Gtk2hs (well-tested though it 
may be) or one of its underlying dependencies (such as libpng).


Tim Newsham
http://www.thenewsh.com/~newsham/
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[Haskell-cafe] Re: universal algebra "support" in Haskell?

[Chung-chieh Shan]

Galchin, Vasili <[EMAIL PROTECTED]> wrote in article <[EMAIL PROTECTED]> in 
gmane.comp.lang.haskell.cafe:
>  Do you have any examples of say "instance Lattice"?

http://web.cecs.pdx.edu/~mpj/pubs/lattices.html
http://web.cecs.pdx.edu/~mpj/pubs/springschool.html

-- 
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You can take the boy out of Harvard, but you can't take the boy's signature...

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[Haskell-cafe] RE: [Haskell] Current XML libraries status

[Mitchell, Neil]

Redirected to haskell-cafe, since that's where all discussions should go
(haskell = announcments only)

> > Does some one have made performance tests on the different XML 
> > libraries for Haskell? I have a 20MB xml file that I want 
> to read. I 
> > remember from my earlier experiments (years ago) that all libraries 
> > were too slow and were consuming too much memory.
> 
> For my XML needs, I ended up just using the TagSoup library 
> to extract the parts I wanted.  At least this allows lazy 
> processing of large files (a typical file is in the 1 to 4 GB range).
> 
> Performance is acceptable, and Neil is rumored to have a plan 
> to improve it further.

I have a plan, I have the pseudo-code, and I have the notes. I currently
don't have the time - but hopefully I'll find the time at some point.

Thanks

Nmeil

==
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Re: [Haskell-cafe] universal algebra "support" in Haskell?

[Henning Thielemann]

On Fri, 24 Oct 2008, Galchin, Vasili wrote:


I "cabal installed" numeric-prelude .. however, unlike other packages(e.g.
Sqlite3), I am unable to ":m numeric-prelude" in a ghci session.??


':m' is for importing modules not packages, at least up to GHC-6.8.2.

For playing around with the package I advice following docs/README.
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Re: [Haskell-cafe] duplicate instance declarations. Why?

[Bulat Ziganshin]

Hello Alberto,

Friday, October 24, 2008, 12:20:39 PM, you wrote:

 >>instance  R a => A a
 >>instance S a => A a 
>   
>  Duplicate instance declarations
>  Why?

because you may write in other module

instance R Int
instance S Int

if class A includes functions, it may be problematic to determine
which implementation (via R or via S) to use


-- 
Best regards,
 Bulatmailto:[EMAIL PROTECTED]

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Re: [Haskell-cafe] duplicate instance declarations. Why?

[Ryan Ingram]

Instance instantiation is *not* search, and *not* similar to
subclassing in OO languages.

Both your instance declarations simply add constraints to functions that use it.

Here's a more concrete example:

class A a where
doA :: a -> String
class R a where
doR :: a -> String

instance R Int where doR = show
instance R a => A a where
doA = doR

question x = doA x

The question is, what is the type of "question"?  Here are two valid
choices with this program:
question :: (A a) => a -> String
question :: (R a) => a -> String

The instance R a => A a says that every type "a" is an instance of
"A"; if an instance for A is needed, the compiler says "OK, I know how
to make one of those.  But I now add a new constraint, R a."

Adding another instance S a => A a makes the choice of what constraint
to add ambiguous.  In particular the following code does *not* work:

class S a where
doS :: a -> String
instance S String where
doS = id
instance S a => A a where
doA = doS

question2 = question (2::Int)
question3 = question "3"

In my experience, if you are turning undecidable instances on and you
don't know exactly why it's safe to do so, there is probably a mistake
in your design.

   -- ryan

2008/10/24 Alberto G. Corona <[EMAIL PROTECTED]>:
> with:
>
>>{-# OPTIONS -fglasgow-exts  -fallow-undecidable-instances  #-}
>
>>class A a
>>class R a
>
>>class S a
>
>>instance  R a => A a
>
>>instance S a => A a
> --
>
> GHC gives
>
> Duplicate instance declarations
>   instance  R a => A a
>   instance S a => A a
>
> Why?
> ___
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>
>
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Re: [Haskell-cafe] Functional MetaPost in 5 Steps

[Robin Green]

On Thu, 23 Oct 2008 22:13:10 -0700
"Jared Updike" <[EMAIL PROTECTED]> wrote:

> I can't even get a simple example to show up in a PDF file

I can't even get my simple example to show up anywhere, period. PDF,
DVI, PS - anything.

No matter which way I try, and I've tried lots, I always hit some kind
of PostScript or TeX error. My Haskell file is attached.

I asked about it on the tex-live mailing list, and I got this
response, advising me to speak to the author:

From: Taco Hoekwater <[EMAIL PROTECTED]>
To: Robin Green <[EMAIL PROTECTED]>
CC: [EMAIL PROTECTED]
Subject: Re: [tex-live] Missing \endcsname errors when trying to insert
MetaPost graphic into PDF Date: Fri, 24 Oct 2008 10:28:20 +0200
User-Agent: Thunderbird 2.0.0.12 (X11/20080305)


Hi Robin,

Robin Green wrote:
> 
> No, it was generated by MetaPost. Here are the sequence of commands I
> used:  

FuncMP.mp is the culprit here. It alters MetaPost's output via
explicit special command so that it is no longer acceptable
to the mptopdf converter.

>> I suggest you rename the file to figure1.eps (and run
>> epstopdf on it before inclusion in your latex document)  
> 
> "epstopdf figure1.eps" outputs this error:
> 
> Error: /undefined in cmmi10  

If the document was was 'plain' metapost input, it would actually
have been possible to fix this in texlive 2008 by adding

   prologues:=3;

at the top of the figure1.mp file.

However, FuncMP.mp has redefined (via specials) the PostScript commands
like /fshow etc,. so this won't work. Also, it seems to be altering
the label typesetting so that it uses metafont bitmap (pk) fonts
instead of type1.

My advice is to look into the functional metapost documentation or
ask its author for help and guidelines on how to use the result
images in pdftex (as opposed to dvips/xdvi).

Best wishes,
Tacoimport FMP (circle, generate, math, text)
import FMP.Tree (edge, enode, node)

fig1 = node (circle $ math "\\lambda")
[ enode (circle $ text "::")
   [ enode (circle $ text "x") []
   , enode (circle $ text "Int") []
   ]
, enode (circle $ text "+")
   [ enode (circle $ text "x") []
   , enode (circle $ text "1") []
   ]
]

main = generate "figure" 1 fig1___
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[Haskell-cafe] darcs hacking sprint TOMORROW!

[Eric Kow]

Hi all,

Just pointing out that the darcs hacking sprint is taking place
tomorrow (Saturday and Sunday 25-26 October)!

Our Brighton and Portland venues are still open, so if you are
thinking of dropping by, let us know :-)

http://wiki.darcs.net/index.html/Sprints

Cheers,

-- 
Eric Kow 
PGP Key ID: 08AC04F9


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[Haskell-cafe] distributed systems reading group

[Jason Dusek]

  I'm looking for good reading group for distributed systems.
  I've worked through a number of papers on my own and would
  like to work out some ideas with other folks who have an
  interest.

  I've read a little bit of Lynch, a bit more of Lamport and
  some of Chandra's work, as well as numerous slides, &c.

 *  The impossibility results are sobering, but always leave a
way out -- they make some assumption that one can dispense
with in practice (for example, that processes start with
different values).

 *  The possibility results generally make untenable assumptions
-- for example, that there is no link failure.

  I appreciate that this is not a matter of direct interest to
  the list, but I expect to find interested people here.

--
_jsn
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[Haskell-cafe] duplicate instance declarations. Why?

[Alberto G. Corona]

with:

>{-# OPTIONS -fglasgow-exts  -fallow-undecidable-instances  #-}

>class A a
>class R a

>class S a

>instance  R a => A a
>instance S a => A a
--

GHC gives

*Duplicate instance declarations*
*  instance  R a => A a *
*  instance S a => A a *
**
*Why?*
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[Haskell-cafe] Re: Sorry, but I'm in the mood (again)

[Achim Schneider]

Benjamin L.Russell <[EMAIL PROTECTED]> wrote:

> On Fri, 24 Oct 2008 07:35:36 +0200, Achim Schneider <[EMAIL PROTECTED]>
> wrote:
> 
> >http://www.haskell.org/haskellwiki/?title=Special:Categories
> >
> >What are the mathematical properties of those Categories? Do they
> >share common axioms? 
> 
> Oh, come on!  Stop talking abstract nonsense (see
> http://en.wikipedia.org/wiki/General_abstract_nonsense) ;-) !
> 
Is sense computable in finite time?


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