date:20100525

On Tuesday 25 May 2010 08:14:13, Ivan Miljenovic wrote:
 On 25 May 2010 16:12, Magicloud Magiclouds

 magicloud.magiclo...@gmail.com wrote:
  Yes, this code works with a little hack. Thank you.

 I'm scared to ask: what pray tell is this little hack?

Looking at it again, probably making it work at all, because I never 
consumed the Log for  lines, so produced an infinite list of empty lists 
:-/

Something like

separateOutput :: String - [[String]]
separateOutput file =
    let contents = dropWhile (not . (Log for  `isPrefixOf`)) $ lines file
split [] = ([],[])
        split (h:tl) = let (lg,rst) = break (Log for  `isPrefixOf`) tl 
   in (h:lg,rst)
        msplit [] = Nothing
        msplit lns = Just (split lns)
    in unfoldr msplit contents

which really works :)
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] How to deal with huge text file?

2010-05-25 Thread Ivan Lazar Miljenovic

Daniel Fischer daniel.is.fisc...@web.de writes:

 On Tuesday 25 May 2010 08:14:13, Ivan Miljenovic wrote:
 On 25 May 2010 16:12, Magicloud Magiclouds

 magicloud.magiclo...@gmail.com wrote:
  Yes, this code works with a little hack. Thank you.

 I'm scared to ask: what pray tell is this little hack?

 Looking at it again, probably making it work at all, because I never 
 consumed the Log for  lines, so produced an infinite list of empty lists 
 :-/

Oh, yeah, I've done that before (with custom chunking functions, etc.).

Just so you know, the split package might already have a function to do
what you want...

-- 
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] [reactive] A pong and integrate

2010-05-25 Thread Limestraël

Wow... impressive...

And now, with your experience, if you'd have to do this again, would you use
Yampa or stick up with C#/C++ ?

2010/5/24 Peter Verswyvelen bugf...@gmail.com

 Yeah. Funny that we're still writing games in C++, while mission
 critical and hard real time systems are written in much nicer
 languages :)

 I made something similar to Lucid Synchrone for a game company I used
 to work, but with the purpose of making reactive programming
 accessible to computer artists. The integrated development environment
 provided the typical boxes-and-links user interface, where the boxes
 were signal functions. Signals itself were not exposed, like Yampa.
 The system did type inference so artists never really had to deal with
 types. Special nodes like feedback and delay where provided to allow
 transferring values to the next frame. This actually was a great
 success, digital artists could literally create little interactive
 applications with it, without much  help from programmers. This
 resulted in a Playstation 3 visual experience Mesmerize
 (http://www.youtube.com/watch?v=rW7qGhBjwhY). This was before I knew
 Haskell or functional programming, so it was hacked together in C# and
 C++...

 I still believe that the reason why computers artists could work with
 this environment and were not able to learn imperative programming is
 functional programming itself: the system had all the goodies of FP:
 type inference, referential transparancy, etc... But is also provided
 the possibility to edit literals while the simulation was running,
 providing zero turnaround times, which was equally important for quick
 adoption of the software.

 So IMO Haskell and FRP systems have a huge potential for education of
 a much broader audience than just computer scientists...





 On Mon, May 24, 2010 at 6:13 PM, Limestraël limestr...@gmail.com wrote:
  I assumed also that it was a field which was still under research,
 however,
  Lustre, again, is used for critical control software in aircraft,
  helicopters, and nuclear power plants, according to wikipedia.

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] How to deal with huge text file?

On Tuesday 25 May 2010 10:44:57, Ivan Lazar Miljenovic wrote:
 Daniel Fischer daniel.is.fisc...@web.de writes:
  On Tuesday 25 May 2010 08:14:13, Ivan Miljenovic wrote:
  On 25 May 2010 16:12, Magicloud Magiclouds
 
  magicloud.magiclo...@gmail.com wrote:
   Yes, this code works with a little hack. Thank you.
 
  I'm scared to ask: what pray tell is this little hack?
 
  Looking at it again, probably making it work at all, because I never
  consumed the Log for  lines, so produced an infinite list of empty
  lists
 
  :-/

 Oh, yeah, I've done that before (with custom chunking functions, etc.).

Who hasn't?


 Just so you know, the split package might already have a function to do
 what you want...

Sort of. Not one function, but the building blocks:

import Data.List (isPrefixOf)
import Data.List.Split

msplit = split (keepDelimsL $ whenElt (Log for  `isPrefixOf`))

I think. But who looks at API docs in the dead of the night when cooking up 
the function seems so easy :)
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] Writing a web service client


Hi, café

I've begun learning Haskell for some time already, and although I don't 
really feel confident writing real world Haskell, I have a little idea 
that I want to materialize in Haskell code so I'm pretty eager to do 
something instead of just reading books and blog posts.


The first step that I want to undertake is to write a client library for 
the GitHub API, so my questions would be:


1. Is there any such library?
2. What other client library should I consider as an API model? Or maybe 
there's some paper/blog post on how do design a Haskell API?
3. What network package do people use for accessing simple, rest-like 
web services? Network.Curl? If not, which other?


Thanks,
--
Ionuț G. Stan  |  http://igstan.ro
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] TDD in Haskell


Hi,

I'm doing TDD in pretty much all of the languages that I know, and I 
want to introduce it early in my Haskell learning process. I wonder 
though, if there's some established process regarding TDD, not unit testing.


I've heard of QuickCheck and HUnit, but I've also read that QuickCheck 
is used mostly for testing pure code, while HUnit for impure code?


What framework lends itself better for writing tests before the actual 
production code? Can you point out to some resources regarding this?



Oh, and a small off-topic question? Is it considered a good practice to 
use implicit imports in Haskell? I'm trying to learn from existing 
packages, but all those import all statements drive me crazy.


Thanks,
--
Ionuț G. Stan  |  http://igstan.ro
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] TDD in Haskell

2010-05-25 Thread Liam O'Connor

QuickCheck is great for TDD. I have used it for such purposes. You
literally encode the contract of the function as quickcheck
properties. It's very lovely.
Cheers.
~Liam



 On 25 May 2010 21:36, Ionut G. Stan ionut.g.s...@gmail.com wrote:
 Hi,

 I'm doing TDD in pretty much all of the languages that I know, and I want to
 introduce it early in my Haskell learning process. I wonder though, if
 there's some established process regarding TDD, not unit testing.

 I've heard of QuickCheck and HUnit, but I've also read that QuickCheck is
 used mostly for testing pure code, while HUnit for impure code?

 What framework lends itself better for writing tests before the actual
 production code? Can you point out to some resources regarding this?


 Oh, and a small off-topic question? Is it considered a good practice to use
 implicit imports in Haskell? I'm trying to learn from existing packages, but
 all those import all statements drive me crazy.

 Thanks,
 --
 Ionuț G. Stan  |  http://igstan.ro
 ___
 Haskell-Cafe mailing list
 Haskell-Cafe@haskell.org
 http://www.haskell.org/mailman/listinfo/haskell-cafe


___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] TDD in Haskell

On Tuesday 25 May 2010 13:36:01, Ionut G. Stan wrote:
 Hi,

 I'm doing TDD in pretty much all of the languages that I know, and I
 want to introduce it early in my Haskell learning process. I wonder
 though, if there's some established process regarding TDD, not unit
 testing.

 I've heard of QuickCheck and HUnit, but I've also read that QuickCheck
 is used mostly for testing pure code, while HUnit for impure code?

And ghci or hugs are the most used tools for testing, be the code pure or 
impure.


 What framework lends itself better for writing tests before the actual
 production code? Can you point out to some resources regarding this?

You can write the QuickCheck properties that your functions should satisfy 
before implementing the functions.
However, when you've determined the specs, it's rather unimportant whether 
you write the properties first or the functions, IMO.



 Oh, and a small off-topic question? Is it considered a good practice to
 use implicit imports in Haskell?

Generally, no. It's considered good practice to use explicit import (and 
export, of course) lists. But as lazy programmers, we can't always resist 
the temptation to skip some not strictly necessary work.
The implicit import of the entire Prelude is a special case, modules from 
the same package are edge cases, but otherwise it's a code smell.

 I'm trying to learn from existing
 packages, but all those import all statements drive me crazy.

 Thanks,

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Writing a web service client

2010-05-25 Thread Vo Minh Thu

2010/5/25 Ionut G. Stan ionut.g.s...@gmail.com:
 Hi, café

 I've begun learning Haskell for some time already, and although I don't
 really feel confident writing real world Haskell, I have a little idea that
 I want to materialize in Haskell code so I'm pretty eager to do something
 instead of just reading books and blog posts.

 The first step that I want to undertake is to write a client library for the
 GitHub API, so my questions would be:

 1. Is there any such library?
 2. What other client library should I consider as an API model? Or maybe
 there's some paper/blog post on how do design a Haskell API?
 3. What network package do people use for accessing simple, rest-like web
 services? Network.Curl? If not, which other?


Hi,

1. I don't think so.
2. Maybe Twidge, on hackage [1]
3. Have also a look at Network.Browser [2]

Cheers,
Thu

[1] http://hackage.haskell.org/package/twidge
[2] 
http://hackage.haskell.org/packages/archive/HTTP/latest/doc/html/Network-Browser.html
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] TDD in Haskell

2010-05-25 Thread Serguey Zefirov

 I'm doing TDD in pretty much all of the languages that I know, and I want to
 introduce it early in my Haskell learning process. I wonder though, if
 there's some established process regarding TDD, not unit testing.

TDD can be deciphered as Type Driven Design, and right now not so many
languages would allow you to experience this.

Take a look at this previous post here:
http://www.haskell.org/pipermail/haskell-cafe/2010-May/077154.html
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Writing a web service client

Hello,

Thanks for all the links. It seems that I have a lot to study before I
produce a decent library :)

The Network.HTTP package looks nice too. It seems to be at the right
level of abstraction compared to Network.Browser.

I have to get used with searching the Hackage repository... :)

On 5/25/10 3:12 PM, Christopher Done wrote:

Hello Ionut,

On 25 May 2010 13:26, Ionut G. Stanionut.g.s...@gmail.com wrote:

The first step that I want to undertake is to write a client library for the
GitHub API, so my questions would be:

1. Is there any such library?

I don't know of nor have seen such a library on Hackage or Github.
There was some brief talk on StackOverflow[1], but nothing about a
full library. I would be interested in using such a library as I am an
enthusiastic user of Github.

[1]:
http://stackoverflow.com/questions/1816092/using-the-github-gist-api-from-haskell

2. What other client library should I consider as an API model? Or maybe
there's some paper/blog post on how do design a Haskell API?

There are some good examples of Haskell code that uses REST-ish
APIs.[1][2][3][4]

Regarding designing a Haskell API, Real World Haskell has some
chapters about that.[5]

My personal advice would be at least to ensure you make it
cabal-install-able, so that entails having a proper cabal file,
documented with Haddock format, with QuickCheck test cases if
appropriate, and provide one or two examples in the documentation, see
Don's guide about writing a Haskell program[8].

[1]: http://hackage.haskell.org/package/flickr
[2]: http://hackage.haskell.org/package/twitter
[3]: http://hackage.haskell.org/package/feed-cli
[4]: http://hackage.haskell.org/package/Bitly
[5]:
http://book.realworldhaskell.org/read/writing-a-library-working-with-json-data.html
[6]:
http://book.realworldhaskell.org/read/io-case-study-a-library-for-searching-the-filesystem.html
[7]:
http://book.realworldhaskell.org/read/advanced-library-design-building-a-bloom-filter.html
[8]: http://www.haskell.org/haskellwiki/How_to_write_a_Haskell_program

3. What network package do people use for accessing simple, rest-like web
services? Network.Curl? If not, which other?

Network.Curl is OK but it relies on a C library which is another
dependency and it's maybe preferable to use the HTTP library or
similar library written in pure Haskell, that you can find on Hackage.

--
Ionuț G. Stan | http://igstan.ro
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] TDD in Haskell

2010-05-25 Thread Christopher Done

On 25 May 2010 13:36, Ionut G. Stan ionut.g.s...@gmail.com wrote:
 I'm doing TDD in pretty much all of the languages that I know, and I want to
 introduce it early in my Haskell learning process. I wonder though, if
 there's some established process regarding TDD, not unit testing.

 I've heard of QuickCheck and HUnit, but I've also read that QuickCheck is
 used mostly for testing pure code, while HUnit for impure code?

 What framework lends itself better for writing tests before the actual
 production code? Can you point out to some resources regarding this?

Real World Haskell has a chapter dedicated to writing Tests for your
code using QuickCheck[1]. The writers of this book work in industries
where well tested programs are essential.

Personally I suppose I follow a methodology of type driven development
followed by tests. I wrote a simple Emacs library to make testing
QuickCheck properties easier[2]. It's convenient because it lets you
check a function when your cursor is at the definition, or test all
properties in the current file. It picks up properties by symbols
named foo_prop, where foo is the function that the foo_prop property
is written for. Maybe this workflow suites your needs.

 Oh, and a small off-topic question? Is it considered a good practice to use
 implicit imports in Haskell? I'm trying to learn from existing packages, but
 all those import all statements drive me crazy.

I would follow tibbe's Haskell style guide[3] because it is strict and
reasonable. To quote it on this topic:

Always use explicit import lists or qualified imports for standard
and third party libraries. This makes the code more robust against
changes in these libraries. Exception: The Prelude.

[1]: http://book.realworldhaskell.org/read/testing-and-quality-assurance.html
[2]: http://www.emacswiki.org/emacs-en/QuickCheckHaskell
[3]: http://github.com/tibbe/haskell-style-guide/blob/master/haskell-style.md
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] TDD in Haskell


On 5/25/10 2:50 PM, Daniel Fischer wrote:

On Tuesday 25 May 2010 13:36:01, Ionut G. Stan wrote:

Hi,

I'm doing TDD in pretty much all of the languages that I know, and I
want to introduce it early in my Haskell learning process. I wonder
though, if there's some established process regarding TDD, not unit
testing.

I've heard of QuickCheck and HUnit, but I've also read that QuickCheck
is used mostly for testing pure code, while HUnit for impure code?


And ghci or hugs are the most used tools for testing, be the code pure or
impure.


Well, probably. I'm looking for an automated solution though. I want to 
be able to rerun the tests on every commit or version release.




What framework lends itself better for writing tests before the actual
production code? Can you point out to some resources regarding this?


You can write the QuickCheck properties that your functions should satisfy
before implementing the functions.
However, when you've determined the specs, it's rather unimportant whether
you write the properties first or the functions, IMO.


It may be true. I've got accustomed though to write code in iterative 
steps, where I first think about the smallest feature that I want to 
implement, then write the test, then again feature - test - code/refactor.


I will certainly have to adapt my work flow within the Haskell way of 
doing things, until then though I'll start from what I know has produced 
good results for me and change it along the way.







Oh, and a small off-topic question? Is it considered a good practice to
use implicit imports in Haskell?


Generally, no. It's considered good practice to use explicit import (and
export, of course) lists. But as lazy programmers, we can't always resist
the temptation to skip some not strictly necessary work.
The implicit import of the entire Prelude is a special case, modules from
the same package are edge cases, but otherwise it's a code smell.



I thought so. Good to know.


I'm trying to learn from existing
packages, but all those import all statements drive me crazy.

Thanks,


___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe



Thanks,
--
Ionuț G. Stan  |  http://igstan.ro
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] TDD in Haskell

2010-05-25 Thread Ben Millwood

On Tue, May 25, 2010 at 12:36 PM, Ionut G. Stan ionut.g.s...@gmail.com wrote:

 Oh, and a small off-topic question? Is it considered a good practice to use
 implicit imports in Haskell? I'm trying to learn from existing packages, but
 all those import all statements drive me crazy.


It's pretty common but I don't like it. Whenever I have to debug
someone else's code usually the first thing I'll do is make all the
import lists explicit so I can work out where a troublesome function
is coming from, and that's a bit of a waste of time.

In some cases though it can get a little silly. Here is an import
statement from one of my projects:

import Language.Haskell.Exts (
 Alt (Alt),
 Binds (BDecls),
 Decl (PatBind, FunBind, InfixDecl),
 Exp (App, Case, Con, Do, If, InfixApp, Lambda, LeftSection,
  Let, List, Lit, Paren, RightSection, Tuple, Var, XPcdata),
 GuardedAlt (GuardedAlt),
 GuardedAlts (UnGuardedAlt, GuardedAlts),
 Literal (Char, Frac, Int, String),
 Match (Match),
 Op (ConOp, VarOp),
 Pat (PApp, PInfixApp, PList, PLit, PParen, PTuple, PVar, PWildCard),
 Name (Ident, Symbol),
 QName (Special, UnQual),
 QOp (QConOp, QVarOp),
 Rhs (UnGuardedRhs),
 SpecialCon (Cons),
 SrcLoc (), -- (SrcLoc),
 Stmt (Generator, LetStmt, Qualifier),
 preludeFixities,
 prettyPrint
 )

...there comes a certain point where one can probably leave the
biggest import implicit, on the basis that if it's from nowhere else,
it's probably there.
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] TDD in Haskell

2010-05-25 Thread Neil Brown


On 25/05/10 12:36, Ionut G. Stan wrote:

Hi,

I'm doing TDD in pretty much all of the languages that I know, and I 
want to introduce it early in my Haskell learning process. I wonder 
though, if there's some established process regarding TDD, not unit 
testing.


I've heard of QuickCheck and HUnit, but I've also read that QuickCheck 
is used mostly for testing pure code, while HUnit for impure code?


I tend to use HUnit more than QuickCheck (even for pure code), but that 
may be a reflection of the projects I've worked on.  Reasons why I have 
used HUnit:


- Writing an Arbitrary instance for a data type wasn't worth the 
effort.  When writing a nanopass compiler, it seemed like too much 
effort to write an Arbitrary instance to produce a valid fragment of AST 
for that particular pass (given that each pass would probably need a 
different instance).  Problems with the instance include:


  * If I allowed every instance to generate the full variety of AST 
elements, the chances of generating an AST fragment that tested the pass 
in question would be vanishingly small, which would require customising 
the instance (or adding generation conditions) in fiddly ways for each 
pass to make sure I got good coverage.


  * For most passes, the AST must obey many pre-conditions, such as all 
variables being declared before use, all expressions type-checking, 
passing various safety/sanity checks and so on.  All these (and 
different sets of them) would need to be considered for each Arbitrary 
instance, which adds a lot of effort to the instance generation, when I 
can easily craft a few targeted pieces of input myself.


- With some functions I can provide an exhaustive check of all inputs, 
for which QuickCheck is ill-suited.  This would suit SmallCheck and 
LazySmallCheck, but often it's just easier to write something like: 
assertTrue $ and [checkResult x (f x) | x - allInputs] than to use the 
other frameworks.


- For QuickCheck 1, testing of things like IO actions was very difficult 
(I think unsafePerformIO was needed?) but QuickCheck 2 is much better in 
that regard once you've gone the hang of it.


More generally, I often think it is less effort to test the corner/edge 
cases carefully with HUnit than it is to express the properties of the 
function (and the properties are almost always noticeably longer than 
the function being tested) and construct an Arbitrary instance that 
produces valid input.  Perhaps I just haven't worked on the right 
projects for QuickCheck or haven't got into the property-based testing 
mindset, though.


Thanks,

Neil.
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] TDD in Haskell

On Tuesday 25 May 2010 14:36:46, Ionut G. Stan wrote:
 On 5/25/10 2:50 PM, Daniel Fischer wrote:
  On Tuesday 25 May 2010 13:36:01, Ionut G. Stan wrote:
  Hi,
 
  I'm doing TDD in pretty much all of the languages that I know, and I
  want to introduce it early in my Haskell learning process. I wonder
  though, if there's some established process regarding TDD, not unit
  testing.
 
  I've heard of QuickCheck and HUnit, but I've also read that
  QuickCheck is used mostly for testing pure code, while HUnit for
  impure code?
 
  And ghci or hugs are the most used tools for testing, be the code pure
  or impure.

 Well, probably. I'm looking for an automated solution though. I want to
 be able to rerun the tests on every commit or version release.


Good practice. You can configure darcs to run the tests on every record (or 
version-tag or whatever).
The testing in ghci/hugs is primarily done while writing the code, after 
that QuickCheck takes over.

  What framework lends itself better for writing tests before the
  actual production code? Can you point out to some resources regarding
  this?
 
  You can write the QuickCheck properties that your functions should
  satisfy before implementing the functions.
  However, when you've determined the specs, it's rather unimportant
  whether you write the properties first or the functions, IMO.

 It may be true. I've got accustomed though to write code in iterative
 steps, where I first think about the smallest feature that I want to
 implement, then write the test, then again feature - test -
 code/refactor.

 I will certainly have to adapt my work flow within the Haskell way of
 doing things, until then though I'll start from what I know has produced
 good results for me and change it along the way.


You will have to adapt your way of thinking about your tasks to Haskell 
(discover new fun ways of doing things :D), but I see no reason why you 
should stop writing the tests first.
What I meant is, once you know what the function should do, it's not 
important whether you write the Quickcheck property before the function or 
the other way round - you can't run the tests before both are written 
anyway :)
Of course, if you write the tests first, you don't risk omitting them.

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] currying combinators


Hi all,

I've posted some code on hpaste

http://www.hpaste.org/fastcgi/hpaste.fcgi/view?id=25694

in which I attempt to develop a currying combinator library.

I'm stuck at some point and would appreciate any help.

Günther

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] [ANNOUNCE] SyntaxMacros-0.1

2010-05-25 Thread Marcos Viera

We are pleased to announce the first release of SyntaxMacros [1].
SyntaxMacros is an EDSL for constructing compilers out of a collection of
pre-compiled,
statically type-checked, possibly mutually dependent ``language-definition
fragments''.
This way of constructing a compiler brings syntax macros for free.

This approach is based on a collection of techniques we have previously
developed:
 - transformation of typed abstract syntax trees [2] makes it possible to
construct parsers on the fly in a type-safe way
 - parser combinators [3] make it possible to construct parsers dynamically
 - first-class attribute grammars [4] make it possible to define semantics
in a compositional way

More information can be found at:
http://www.cs.uu.nl/wiki/Center/SyntaxMacrosForFree

Regards,

Marcos Viera, Doaitse Swierstra, Atze Dijkstra and Arthur Baars


[1]- http://hackage.haskell.org/package/SyntaxMacros
[2]- http://www.cs.uu.nl/wiki/Center/TTTAS
[3]- http://www.cs.uu.nl/wiki/bin/view/HUT/ParserCombinators
[4]- http://www.cs.uu.nl/wiki/Center/AspectAG
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Writing a web service client

2010-05-25 Thread Mike Dillon

I've been playing around with creating a binding for Zenfolio's JSON-RPC
API for the last few days. I've been looking at Sigbjorn Finne's
excellent packages on Hackage for guidance, including flickr, delicious,
and hs-twitter. I've also been looking at HTTP's Network.Browser and
HAXR's Network.XmlRpc since I'm having to implement the underying
JSON-RPC protocol too (again based on Sigbjorn's excellent json
package).

-md

begin Ionut G. Stan quotation:
Hello,

Thanks for all the links. It seems that I have a lot to study before
I produce a decent library :)

The Network.HTTP package looks nice too. It seems to be at the right
level of abstraction compared to Network.Browser.

I have to get used with searching the Hackage repository... :)

On 5/25/10 3:12 PM, Christopher Done wrote:
Hello Ionut,

On 25 May 2010 13:26, Ionut G. Stanionut.g.s...@gmail.com wrote:
The first step that I want to undertake is to write a client library for the
GitHub API, so my questions would be:

1. Is there any such library?

[1]:
http://stackoverflow.com/questions/1816092/using-the-github-gist-api-from-haskell

2. What other client library should I consider as an API model? Or maybe
there's some paper/blog post on how do design a Haskell API?

There are some good examples of Haskell code that uses REST-ish
APIs.[1][2][3][4]

Regarding designing a Haskell API, Real World Haskell has some
chapters about that.[5]

3. What network package do people use for accessing simple, rest-like web
services? Network.Curl? If not, which other?

Network.Curl is OK but it relies on a C library which is another
dependency and it's maybe preferable to use the HTTP library or
similar library written in pure Haskell, that you can find on Hackage.

--
Ionuț G. Stan | http://igstan.ro
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Haskell, Queries and Monad Comprehension

2010-05-25 Thread Markus Läll

I would be intrested in seeing this! Could you paste or upload it somewhere?


2010/5/24 C. McCann c...@uptoisomorphism.net:
 2010/5/23 Günther Schmidt gue.schm...@web.de:
 is there anybody currently using Haskell to construct or implement a query
 language?

 I've a half-baked, type-indexed (in HList style) implementation of
 relational algebra lying around somewhere, if that counts as a query
 language. I was experimenting with using it as a sort of abstract
 collection interface, which actually worked rather nicely I think, but
 I didn't have time to flesh it out completely. In particular, only
 very simple queries and limited kinds of relation composition were
 supported. Definitely just toy code, though, and dreadfully
 inefficient; if you're looking for an actual implementation meaning
 usable interface to an external persistence layer then disregard
 this.

 - C.
 ___
 Haskell-Cafe mailing list
 Haskell-Cafe@haskell.org
 http://www.haskell.org/mailman/listinfo/haskell-cafe

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] currying combinators

2010-05-25 Thread Yitzchak Gale

Günther Schmidt wrote:
 http://www.hpaste.org/fastcgi/hpaste.fcgi/view?id=25694
 in which I attempt to develop a currying combinator library.
 I'm stuck at some point and would appreciate any help.

How about this:

keep :: ((t - b) - u - b) - ((t1 - t) - b) - (t1 - u) - b

so then

nameZip = keep (drop' . drop') names

Regards,
Yitz
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

RE: [Haskell-cafe] Re: Data instance for a GADT

2010-05-25 Thread Simon Peyton-Jones

There have been a couple of emails about Template Haskell support for

· GADTs

· View patterns

· Reifying instances

There’s a ticket for this already 
http://hackage.haskell.org/trac/ghc/ticket/3497

It’s mainly a library design question, in this case the design of the Template 
Haskell data types in Language.Haskell.TH.Syntax.  It needs some motivated 
person to propose a design, get a consensus, and write some boilerplate code.   
Just use the standard libraries process

An issue is the extent to which it’s ok to change the Template Haskell data 
types (and thereby break people’s code), but that’s something the interested 
parties can work out together.

If you evolve a consensus design I’m more than happy to make it part of GHC. I 
just don’t want to drive the consensus building!

Simon

From: haskell-cafe-boun...@haskell.org 
[mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Ozgur Akgun
Sent: 14 April 2010 10:53
To: Haskell cafe
Subject: [Haskell-cafe] Re: Data instance for a GADT

Seeing this old thread[1], I hope something happened towards enabling this.
Does anybody know the current status about using TH on GADTs?

[1] http://www.haskell.org/pipermail/template-haskell/2006-August/000567.html

On 14 April 2010 10:32, Ozgur Akgun 
ozgurak...@gmail.commailto:ozgurak...@gmail.com wrote:
answering to myself: I guess this is related: 
http://hackage.haskell.org/trac/ghc/ticket/3497

On 14 April 2010 10:13, Ozgur Akgun 
ozgurak...@gmail.commailto:ozgurak...@gmail.com wrote:
Cafe,

How can I provide a Data instance for a GADT? I am trying to TH on it, and 
Uniplate requires Data.
I tried StandaloneDeriving, but it seems not to work.

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] TDD in Haskell

2010-05-25 Thread Stephen Tetley

On 25 May 2010 13:25, Christopher Done chrisd...@googlemail.com wrote:

 I would follow tibbe's Haskell style guide[3] because it is strict and
 reasonable. To quote it on this topic:

 Always use explicit import lists or qualified imports for standard
 and third party libraries. This makes the code more robust against
 changes in these libraries. Exception: The Prelude.

 [3]: http://github.com/tibbe/haskell-style-guide/blob/master/haskell-style.md


The possible advantage in robustness is pretty small - if the imported
library adds and exports a new definition using a name you were
already using then you'll get a name conflict.

The GHC style guide has better[*] reasons for avoiding them:

http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle


[*] Better - as in it conforms to my prejudice

Best wishes

Stephen
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Exception: : changeWorkingDirectory: does not exist (No such file or directory)

2010-05-25 Thread Anatoly Yakovenko

there must have been some linker incompatibility.  gentoo must have
updated some library that ghci depended on causing this breakage.  I
re-installed ghc and everything started working.

On Mon, May 24, 2010 at 1:19 PM, Daniel Fischer
daniel.is.fisc...@web.de wrote:
 On Monday 24 May 2010 21:35:10, Anatoly Yakovenko wrote:
 :set -fglasgow-exts

 Can't you be more discriminating and turn on only those extensions you
 regularly use?

 :set prompt  

 Thats all i have in my .ghci file

 Shouldn't cause a cd.

 Maybe

 $ ghci -v4

 would give a hint?

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Declaring a tuple of instances of Enums as an instance of the Enum class

2010-05-25 Thread Henning Thielemann

Daniel Fischer schrieb:
 On Sunday 23 May 2010 15:33:58, Ivan Lazar Miljenovic wrote:
 R J rj248...@hotmail.com writes:
 Say I've got a type Month declared as an instance of the Enum
 class, and a type MonthPair declared as a pair of months:
 data Month = January | February | March | April | May | June | July |
 August | September | October | November | December deriving (Eq, Enum,
 Ord, Show)
 type MonthPair = (Month, Month) deriving (Enum)
 The deriving on MonthPair gives me the error parse error on input
 deriving'.
 You can't derive instances for type aliases (as its mainly there for
 documentation reasons, etc.).  However, pairs don't have Enum instances
 by default so you still can't use its instance.

 If you define data MonthPair = MonthPair Month Month then you should
 be able to derive Enum.
 
 No, per the report (http://haskell.org/onlinereport/derived.html)
 
 Derived instance declarations for the class Enum are only possible for 
 enumerations (data types with only nullary constructors).

You might define an instance more generally:

data EnumPair a b = EnumPair a b

instance (Enum a, Bounded b, Enum b) = Enum (EnumPair a b) where
   ...

Then define something like
  fromEnum (EnumPair a b) = (maxBound - minBound)*a + b

(needs still some asTypeOf's and fromEnum's)

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] MultiParamClasses question

2010-05-25 Thread Eugeny N Dzhurinsky

Hello, all!

I'm trying to create set of polymorphic functions for working with custom
containers. I decided to try out typeclass and define generic function, which
uses the methods from the typeclass. The quick and naive solution is listed
below:


{-# OPTIONS_GHC -XMultiParamTypeClasses -XTypeSynonymInstances #-}
import Data.List as L

class Storage k t a b where
stExists :: k - t - b - Bool
stAdjust :: k - t - ( a - a ) - b - b
stInsert :: k - t - a - b - b
stList :: b - [a]

type IxPair k t = ( k, t, String, String)

data Pair = Pair { name, value :: String }

type IxPairParser k t = Pair - Maybe (IxPair k t)

type RecordUpdateF r = String - String - r - r

convertPairsToRecords :: (Storage k t a b) = b - RecordUpdateF a - 
IxPairParser k t - a - [Pair] - [a]
convertPairsToRecords storg updateRecF parsePairF initRec = stList . 
processWithPairs
where
processWithPairs = foldl' ( (. parsePairF) . updateStorage ) storg
updateStorage st Nothing = st
updateStorage st ( Just (idx, sType, name, value) ) | stExists idx 
sType st = stAdjust idx sType (updateRecF name value) st
| otherwise = 
stInsert idx sType (updateRecF name value initRec) st


so I want to provide methods for checking if a record with given key exists,
update a record, insert a record and get list of records. Sounds similar as
for Map, but I want also to be able to operate on map of maps, or lists, or
whatever.

I don't really see any problem with the code above, however GHC 6.12.1 does
think that I am doing something weird. And it gives me this error log:


test.hs:19:60:
Could not deduce (Storage k t a1 b)
  from the context (Storage k1 t1 a1 b)
  arising from a use of `stList' at test.hs:19:60-65
Possible fix:
  add (Storage k t a1 b) to the context of
the type signature for `convertPairsToRecords'
In the first argument of `(.)', namely `stList'
In the expression: stList . processWithPairs
In the definition of `convertPairsToRecords':
convertPairsToRecords storg updateRecF parsePairF initRec
= stList . processWithPairs
where
processWithPairs = foldl' ((. parsePairF) . 
updateStorage) storg
updateStorage st Nothing = st
updateStorage st (Just (idx, sType, name, 
value))
| stExists idx sType st
= stAdjust idx sType 
(updateRecF name value) st
| otherwise
= stInsert
idx sType (updateRecF 
name value initRec) st

test.hs:21:53:
Could not deduce (Storage k1 t1 a b)
  from the context (Storage k1 t1 a1 b)
  arising from a use of `updateStorage' at test.hs:21:53-65
Possible fix:
  add (Storage k1 t1 a b) to the context of
the type signature for `convertPairsToRecords'
In the second argument of `(.)', namely `updateStorage'
In the first argument of `foldl'', namely
`((. parsePairF) . updateStorage)'
In the expression: foldl' ((. parsePairF) . updateStorage) storg


Can somebody please advice, what am I doing in wrong way?

Thank you all in advance!

-- 
Eugene Dzhurinsky


pgpzU1NdMQ3jN.pgp
Description: PGP signature
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] MultiParamClasses question

2010-05-25 Thread Stephen Tetley

Hi Eugeny

Its not that GHC thinks you're doing something weird, but that there
is no relation between the type parameters in the Storage class. You
could use either functional dependencies or type families to introduce
a relation / relations, but personally I would look at doing something
simpler - for instance why do you need a map type that is polymorphic
on shape?

Best wishes

Stephen
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] Re: Cabal sqlite3 installation problems

2010-05-25 Thread Ben

i have this exact problem, on linux x86_64, as well.

b

Hok Shun Poon fushunpoon at googlemail.com
Sun May 23 19:51:20 EDT 2010
Previous message: memory useage of data types in the time package
Next message: Text.Regex library with bytestrings?
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Hello,

This is a question about how cabal-install finds 'installed foreign
libraries' when trying to satisfy dependencies for packages like
hdbc-sqlite3 on Windows.
Sadly, the current setup means that I must use Windows 7 to develop code.

I've already followed steps on
http://wiki.github.com/jgoerzen/hdbc/frequentlyaskedquestions to place the
.dll and the .h files in the correct places; it's just that cabal never
seems to find it, despite being given --extra-lib-dirs= and
--extra-include-dirs= directives.

The message is as follows:

 cabal install hdbc-sqlite3 --extra-lib-dirs=D:\dev\libs\database\sqlite
Resolving dependencies...
Configuring HDBC-sqlite3-2.3.0.0...
cabal: Missing dependency on a foreign library:
* Missing C library: sqlite3
This problem can usually be solved by installing the system package
that provides this library (you may need the -dev version). If the library
is already installed but in a non-standard location then you can use
the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it
is.
cabal: Error: some packages failed to install:
HDBC-sqlite3-2.3.0.0 failed during the configure step. The exception was:
ExitFailure 1

The strangest thing is, I've successfully made cabal build this package
before (with a different version of Haskell Platform)... what's going on?

I'm using cabal-install version 0.8.2 and Cabal library version 1.8.0.2.

Hok
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] MultiParamClasses question

2010-05-25 Thread Henning Thielemann



On Tue, 25 May 2010, Eugeny N Dzhurinsky wrote:


I'm trying to create set of polymorphic functions for working with custom
containers. I decided to try out typeclass and define generic function, which
uses the methods from the typeclass. The quick and naive solution is listed
below:


There are also frameworks for dealing with different kinds of containers 
like Edison.

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] MultiParamClasses question

On Tuesday 25 May 2010 20:51:06, Eugeny N Dzhurinsky wrote:
 Hello, all!

 I'm trying to create set of polymorphic functions for working with
 custom containers. I decided to try out typeclass and define generic
 function, which uses the methods from the typeclass. The quick and naive
 solution is listed below:

As Stephen said, FunctionalDependencies and TypeFamilies are two options.
The problem is that stList is unusable because there's no way to find out 
which instance to use (determine k and t) from a use of stList.
Also, you can't determine a from a use of stExists, so that's unusable, 
too.

You could make all class parameters depend on b (via FunDeps or 
TypeFamilies), or
- make b a type constructor of kind (* - *) and
- move stList to its own class.

class StList b where
stList :: b a - [a]

class Storage k t b where
stExists :: k - t - b a - Bool
stAdjust :: k - t - (a - a) - b a - b a
stInsert :: k - t - a - b a - b a


 

Don't put language extensions in an OPTIONS_GHC pragma, use a LANGUAGE 
pragma instead.

 {-# OPTIONS_GHC -XMultiParamTypeClasses -XTypeSynonymInstances #-}
 import Data.List as L

 class Storage k t a b where
 stExists :: k - t - b - Bool
 stAdjust :: k - t - ( a - a ) - b - b
 stInsert :: k - t - a - b - b
 stList :: b - [a]

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Haskell, Queries and Monad Comprehension

2010-05-25 Thread Torsten Grust

Günther,

On May 24, 2010, at 03:20 , Günther Schmidt wrote:
 Hi all,
 
 is there anybody currently using Haskell to construct or implement a query 
 language?
 
 I have read a couple of papers on Monad Comprehension Calculus and similar 
 but none using Haskell nor any other existing programming language to build 
 an actual implementation.
 
 Most papers give some sort of Pseudo code, but I couldn't find any meat.

we are currently underway building the second version (as in:
done right this time) of Ferry, a query compiler that 

(1) accepts queries over ordered, nested lists,
(2) compiles these queries into an intermediate algebraic form, then
(3) emits (small bundles of) SQL queries that evaluate the input
   query over your off-the-shelf RDBMS.

We've used Ferry's first version to build new LINQ to SQL providers
for Microsoft's LINQ as well as a new code generator for Phil Wadler's
Links.

The Ferry compiler itself is built in Haskell.  Surf to www.ferry-lang.org
for more information, screencasts, papers, talks, and contact us for
more details.  We will be happy to share Ferry's Haskell code once in 
digestable shape (soon).

Cheers,
  --Torsten

-- 
  | Prof. Dr. Torsten Grust  torsten.gr...@uni-tuebingen.de |
  |  www-db.informatik.uni-tuebingen.de |
  |   Database Systems - Universität Tübingen (Germany) |

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] [reactive] A pong and integrate

2010-05-25 Thread Peter Verswyvelen

Well, first of all, I did not make these PS3 visualization, my former
colleagues and I just made the editor, language and runtime that
allowed video game artists to do the job for us in a couple of weeks
time :-)

I wouldn't use Yampa, for performance reasons, and difficulty to get
it running on alien platforms (it is well known it performs relatively
badly, although the work done by Paul Liu and co on Causal Commutative
Arrows looks very promising, but does not support dynamic switching
yet). After all, Yampa models a synchronous dataflow language, and
compilers for these languages are relatively easy to make IMO.

My previous - now defunct -  company Anygma spent a lot of money on
trying to use Haskell and Reactive for game programming, which
unfortunately ended in some nasty GHC bugs popping up (see
http://www.haskell.org/haskellwiki/Unamb), and not all problems with
Reactive got fixed; it is amazing how difficult this all turned out to
be. The GHC bugs are now fixed, so it might be stable enough for
another adventure like that, but I don't think I would bet on it
again.

IMO Haskell is great for writing small clean prototypes, doing
interesting research, and maybe making some fun little games, but I
wouldn't use it for production reactive game coding, not yet at least.


On Tue, May 25, 2010 at 10:49 AM, Limestraël limestr...@gmail.com wrote:
 Wow... impressive...

 And now, with your experience, if you'd have to do this again, would you use
 Yampa or stick up with C#/C++ ?

 2010/5/24 Peter Verswyvelen bugf...@gmail.com

 Yeah. Funny that we're still writing games in C++, while mission
 critical and hard real time systems are written in much nicer
 languages :)

 I made something similar to Lucid Synchrone for a game company I used
 to work, but with the purpose of making reactive programming
 accessible to computer artists. The integrated development environment
 provided the typical boxes-and-links user interface, where the boxes
 were signal functions. Signals itself were not exposed, like Yampa.
 The system did type inference so artists never really had to deal with
 types. Special nodes like feedback and delay where provided to allow
 transferring values to the next frame. This actually was a great
 success, digital artists could literally create little interactive
 applications with it, without much  help from programmers. This
 resulted in a Playstation 3 visual experience Mesmerize
 (http://www.youtube.com/watch?v=rW7qGhBjwhY). This was before I knew
 Haskell or functional programming, so it was hacked together in C# and
 C++...

 I still believe that the reason why computers artists could work with
 this environment and were not able to learn imperative programming is
 functional programming itself: the system had all the goodies of FP:
 type inference, referential transparancy, etc... But is also provided
 the possibility to edit literals while the simulation was running,
 providing zero turnaround times, which was equally important for quick
 adoption of the software.

 So IMO Haskell and FRP systems have a huge potential for education of
 a much broader audience than just computer scientists...





 On Mon, May 24, 2010 at 6:13 PM, Limestraël limestr...@gmail.com wrote:
  I assumed also that it was a field which was still under research,
  however,
  Lustre, again, is used for critical control software in aircraft,
  helicopters, and nuclear power plants, according to wikipedia.


___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Haskell, Queries and Monad Comprehension


Hello Torsten,

well thank you for taking the time and answering that. It seems that the 
one thing I am good for, as far as contributions to this list go, is 
coaxing answers out of our Functional Pros. :)


That is good news then, I was getting frustrated reading fantastic 
papers which eventually were nothing more than teasers.


So, will Ferry then be usable from within Haskell?

Best regards

Günther



Am 25.05.10 21:28, schrieb Torsten Grust:
 Günther,

 we are currently underway building the second version (as in:
 done right this time) of Ferry, a query compiler that

 (1) accepts queries over ordered, nested lists,
 (2) compiles these queries into an intermediate algebraic form, then
 (3) emits (small bundles of) SQL queries that evaluate the input
  query over your off-the-shelf RDBMS.

 We've used Ferry's first version to build new LINQ to SQL providers
 for Microsoft's LINQ as well as a new code generator for Phil Wadler's
 Links.

 The Ferry compiler itself is built in Haskell.  Surf to 
www.ferry-lang.org

 for more information, screencasts, papers, talks, and contact us for
 more details.  We will be happy to share Ferry's Haskell code once in
 digestable shape (soon).

 Cheers,
 --Torsten

 On May 24, 2010, at 03:20 , Günther Schmidt wrote:
 Hi all,

 is there anybody currently using Haskell to construct or implement a 
query language?


 I have read a couple of papers on Monad Comprehension Calculus and 
similar but none using Haskell nor any other existing programming 
language to build an actual implementation.


 Most papers give some sort of Pseudo code, but I couldn't find any 
meat.




 Günther

 ___
 Haskell-Cafe mailing list
 Haskell-Cafe@haskell.org
 http://www.haskell.org/mailman/listinfo/haskell-cafe




___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Haskell, Queries and Monad Comprehension

2010-05-25 Thread Torsten Grust

Hi Günther,

On May 25, 2010, at 21:37 , Günther Schmidt wrote:
 Hello Torsten,
 
 well thank you for taking the time and answering that. It seems that the one 
 thing I am good for, as far as contributions to this list go, is coaxing 
 answers out of our Functional Pros. :)
 
 That is good news then, I was getting frustrated reading fantastic papers 
 which eventually were nothing more than teasers.
 
 So, will Ferry then be usable from within Haskell?

Ferry is much more about the compilation of queries (over list-based
data models) than the invention of some new query syntax.  We
thus are mostly after embeddings of queries into existing 
host languages.  Such embeddings exist for

  -- C#(Ferry-based LINQ to SQL)
  -- Links (new Ferry-based SQL code generator)
  -- Ruby  (in the works, provides a much richer and arguably more
seamless embedding of queries over Ruby arrays as well
as relational tables than does ARel or ActiveRevord's 
find_by* methods).

There's some interesting connection between the compilation 
techniques employed by Ferry and Data Parallel Haskell.  
I talked to Simon Peyton Jones and he suggested to attempt 
a Haskell embedding.  So, Haskell: not yet.  But conceivable.

Cheers,
   --Torsten

 Am 25.05.10 21:28, schrieb Torsten Grust:
  Günther,
 
  we are currently underway building the second version (as in:
  done right this time) of Ferry, a query compiler that
 
  (1) accepts queries over ordered, nested lists,
  (2) compiles these queries into an intermediate algebraic form, then
  (3) emits (small bundles of) SQL queries that evaluate the input
   query over your off-the-shelf RDBMS.
 
  We've used Ferry's first version to build new LINQ to SQL providers
  for Microsoft's LINQ as well as a new code generator for Phil Wadler's
  Links.
 
  The Ferry compiler itself is built in Haskell.  Surf to www.ferry-lang.org
  for more information, screencasts, papers, talks, and contact us for
  more details.  We will be happy to share Ferry's Haskell code once in
  digestable shape (soon).
 
  Cheers,
  --Torsten
 
  On May 24, 2010, at 03:20 , Günther Schmidt wrote:
  Hi all,
 
  is there anybody currently using Haskell to construct or implement a query 
  language?
 
  I have read a couple of papers on Monad Comprehension Calculus and 
  similar but none using Haskell nor any other existing programming language 
  to build an actual implementation.
 
  Most papers give some sort of Pseudo code, but I couldn't find any meat.
 
 
 
  Günther
 
  ___
  Haskell-Cafe mailing list
  Haskell-Cafe@haskell.org
  http://www.haskell.org/mailman/listinfo/haskell-cafe
 
 
 
 




-- 
  | Prof. Dr. Torsten Grust  torsten.gr...@uni-tuebingen.de |
  |  www-db.informatik.uni-tuebingen.de |
  |   Database Systems - Universität Tübingen (Germany) |

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] Re: Haskell, Queries and Monad Comprehension


2010/5/23 Günther Schmidtgue.schm...@web.de:

is there anybody currently using Haskell to construct or implement a query
language?


I've a half-baked, type-indexed (in HList style) implementation of
relational algebra lying around somewhere, if that counts as a query
language. I was experimenting with using it as a sort of abstract
collection interface, which actually worked rather nicely I think, but
I didn't have time to flesh it out completely. In particular, only
very simple queries and limited kinds of relation composition were
supported. Definitely just toy code, though, and dreadfully
inefficient; if you're looking for an actual implementation meaning
usable interface to an external persistence layer then disregard
this.



Well you're on the radar now :)

BTW: I'm working on alternative, non-type-indexed version of extensible 
records (Which I have gathered to be an essential ingredient when you 
want to roll a Relational Algebra lib). There will be no first-class 
labels, but there also will be no need for singleton-types either (which 
is what you need with type-indexed solutions). And a bit less overhead 
all-around so it's kind making up for not having 1st class labels.



___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] MultiParamClasses question

2010-05-25 Thread Eugeny N Dzhurinsky

On Tue, May 25, 2010 at 07:59:24PM +0100, Stephen Tetley wrote:
 Hi Eugeny
 
 Its not that GHC thinks you're doing something weird, but that there
 is no relation between the type parameters in the Storage class. You
 could use either functional dependencies or type families to introduce
 a relation / relations, but personally I would look at doing something
 simpler - for instance why do you need a map type that is polymorphic
 on shape?

Currently I am creating set of objects from name-value pairs, and I decided to
use Map for keeping relations between an object id and record with the id. So
I will be able to parse the parameter like

param_1_propname=value

then take the object with ID=1 from Map, and update it's property 'propname'
with value, and put it back into the Map.

But I faced several cases when a set of name-value pairs describes  2 or even
more kinds of objects. And I want to be able to parse them all at one pass, so
I would need 2 or more maps. And I simply tried to generalize the solution.

Probably I should think in different way. May be a chain of Writer monads or
something similar.

-- 
Eugene Dzhurinsky


pgpziyjo4T7jQ.pgp
Description: PGP signature
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] Re: Cabal sqlite3 installation problems


Hi Hok,

I know the problem and the only solution I found to work is using an 
older version of cabal.exe. I still have one lying around for these 
cases, in my Path called cabalOld.exe and use it only in situations 
like these.


Lemme know if I should send it to you.

Günther


Am 25.05.10 21:05, schrieb Ben:

i have this exact problem, on linux x86_64, as well.

b

Hok Shun Poon fushunpoon at googlemail.com
Sun May 23 19:51:20 EDT 2010
Previous message: memory useage of data types in the time package
Next message: Text.Regex library with bytestrings?
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Hello,

This is a question about how cabal-install finds 'installed foreign
libraries' when trying to satisfy dependencies for packages like
hdbc-sqlite3 on Windows.
Sadly, the current setup means that I must use Windows 7 to develop code.

I've already followed steps on
http://wiki.github.com/jgoerzen/hdbc/frequentlyaskedquestions to place the
..dll and the .h files in the correct places; it's just that cabal never
seems to find it, despite being given --extra-lib-dirs= and
--extra-include-dirs= directives.

The message is as follows:


cabal install hdbc-sqlite3 --extra-lib-dirs=D:\dev\libs\database\sqlite

Resolving dependencies...
Configuring HDBC-sqlite3-2.3.0.0...
cabal: Missing dependency on a foreign library:
* Missing C library: sqlite3
This problem can usually be solved by installing the system package
that provides this library (you may need the -dev version). If the library
is already installed but in a non-standard location then you can use
the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it
is.
cabal: Error: some packages failed to install:
HDBC-sqlite3-2.3.0.0 failed during the configure step. The exception was:
ExitFailure 1

The strangest thing is, I've successfully made cabal build this package
before (with a different version of Haskell Platform)... what's going on?

I'm using cabal-install version 0.8.2 and Cabal library version 1.8.0.2.

Hok



___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] [ANNOUNCE] SyntaxMacros-0.1

2010-05-25 Thread Oscar Finnsson

 We are pleased to announce the first release of SyntaxMacros [1].

Very interesting. This is something I've been interested in since I
first heard of Ziggurat.

In which order do you recommend I try to learn the packages: HList -
AspectAG - SyntaxMacros?

I tried to read the SyntaxMacros-paper but had a hard time
understanding which parts belonged to the package and which parts
belonged to your new mini-language. Do you got the mini-language as a
separate download?

You mention in the paper that the source of the paper is in literate
Haskell and that the code is available but I can't find it at the
wiki.  I found some code (Expr.hs, Main.hs) in the examples-folder in
the packages source code (SyntaxMacrox-0.1.tar.gz) but it doesn't seem
to match 1:1 to the code in the paper (couldn't for example find
extSpecChars in the paper or updateFinalEnv in the source code).

-- Oscar
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] MultiParamClasses question

2010-05-25 Thread Stephen Tetley

Hi Eugene


You can store different things in a Map by collecting them with a
simple 'sum' type:

 import qualified Data.Map as Map

 type DateTime = String-- just String for now..
 type URL  = String
 type UniqueID = String

Here's the sum type:

 data LogData = LastLogin DateTime
  | LastLogout DateTime
  | ReferringURL URL
   deriving (Eq, Show)


 type ExtraInfo = Map.Map UniqueID [LogData]

 addData :: UniqueID - LogData - ExtraInfo - ExtraInfo
 addData uid prop infos = case Map.lookup uid infos of
 Nothing - Map.insert uid [prop]infos
 Just xs - Map.insert uid (prop:xs) infos

Note - this stores all the LastLogin's ReferringURLS etc. As the list
is LIFO the first @LastLogin@ in the list will be the latest
one.

If you don't like storing multiples, you could instead recast LogData
as a record rather than sum  type, but you then have to
account for 'missing' data with Maybe's.

 data LogData2 = LogData2
   { last_login:: Maybe DateTime
   , last_logout   :: Maybe DateTime
   , referring_URL :: Maybe URL
   }

 emptyLogData2 :: LogData2
 emptyLogData2 = LogData2 Nothing Nothing Nothing

 type ExtraInfo_ALT = Map.Map UniqueID LogData2

 addLastLogin :: UniqueID - DateTime - ExtraInfo_ALT - ExtraInfo_ALT
 addLastLogin uid lasttime infos = case Map.lookup uid infos of
 Nothing  - Map.insert uid (emptyLogData2 { last_login = Just lasttime}) 
 infos
 Just ld2 - Map.insert uid (ld2 { last_login = Just lasttime}) infos


Make similar functions for last_logout, referring_url.

Best wishes

Stephen
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] Math questions

2010-05-25 Thread Mujtaba Boori

Hello
I am try to solve this equation

Define a higher order function  that tests whether two functions , both
defined on integers , coincide for all integers between 1 and 100

 how can I solve this ?
is there any thing in Haskell library to solve this kind ?

-- 
Mujtaba Ali Alboori
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Math questions

2010-05-25 Thread caseyh


Quoting Mujtaba Boori mujtaba.bo...@gmail.com:


Hello
I am try to solve this equation

Define a higher order function  that tests whether two functions , both
defined on integers , coincide for all integers between 1 and 100

 how can I solve this ?
is there any thing in Haskell library to solve this kind ?

--
Mujtaba Ali Alboori



This sounds like homework.

In any case, won't your HOF take as input the two functions and the  
input range to check.

Then think about how you might compare the output of the two functions.


___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Math questions

On Tuesday 25 May 2010 23:47:30, Mujtaba Boori wrote:
 Hello
 I am try to solve this equation

 Define a higher order function  that tests whether two functions , both
 defined on integers , coincide for all integers between 1 and 100

  how can I solve this ?
 is there any thing in Haskell library to solve this kind ?

Sure. Lots of things to do it in different ways. All boil down to
- for each integer from 1 to 100
- check whether f i == g i

Look at
http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Prelude.html
, there are  useful functions for this. You will probably want to use 'and' 
or 'all'.

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] Math questions

2010-05-25 Thread Mujtaba Boori

Thank you all you , that is really impressive .


I will read your response carefully , and  I think this it is enough to
understand it.

On 25 May 2010 23:43, Daniel Fischer daniel.is.fisc...@web.de wrote:

 On Tuesday 25 May 2010 23:47:30, Mujtaba Boori wrote:
  Hello
  I am try to solve this equation
 
  Define a higher order function  that tests whether two functions , both
  defined on integers , coincide for all integers between 1 and 100
 
   how can I solve this ?
  is there any thing in Haskell library to solve this kind ?

 Sure. Lots of things to do it in different ways. All boil down to
 - for each integer from 1 to 100
 - check whether f i == g i

 Look at

 http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Prelude.html
 , there are  useful functions for this. You will probably want to use 'and'
 or 'all'.




-- 
Mujtaba Ali Alboori
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] TagSoup 0.9

2010-05-25 Thread Neil Mitchell

Hi,

From what I can tell of your example you've managed to get the raw
HTTP response in Unicode, which isn't suitable for sending to tagsoup.
I've not used the Network.HTTP library for downloading much, but when
I did I thought it stripped the headers automatically.

Can you just print the first few lines of the output you get from the
HTTP library, without passing them through tagsoup. That should show
the problem independent of tagsoup.

Thanks, Neil

On Mon, May 24, 2010 at 3:24 AM, Ralph Hodgson rhodg...@topquadrant.com wrote:
Thanks Neil,

Using Network.HTTP worked.

However something else I have just run into concerns some web pages that
start with:

?xml version=1.0 encoding=iso-8859-1?

!DOCTYPE html PUBLIC -//W3C//DTD XHTML 1.0 Transitional//EN
http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd;

I get the following bad result:

TagText HTTP/1.1 200 OK\r\nContent-Type: text/html\r\nLast-Modified: Tue,
27 Oct 2009 19:30:40 GMT\r\nETag: \6f248cf73b57ca1:25e2\\r\nDate: Sun, 23
May 2010 22:46:41 GMT\r\nTransfer-Encoding: chunked\r\nConnection:
close\r\nConnection:
Transfer-Encoding\r\n\r\n4000\r\n\255\254\NUL?\NULx\NULm\NULl\NUL
\NULv\NULe\NULr\NULs\NULi\NULo\NULn\NUL=\NUL\\NUL1\NUL.\NUL0\NUL\\NUL
\NULe\NULn\NULc\NULo\NULd\NULi\NULn\NULg\NUL=\NUL\\NULi\NULs\NULo\NUL-\NUL8\NUL8\NUL5\NUL9\NUL-\NUL1\NUL\\NUL

etc etc

Is this an easy thing to fix? I've started to look over the code.

-Original Message-
From: Neil Mitchell [mailto:ndmitch...@gmail.com]
Sent: Wednesday, May 19, 2010 12:19 PM
To: Ralph Hodgson
Cc: Daniel Fischer; haskell-cafe@haskell.org; Don Stewart
Subject: Re: [Haskell-cafe] TagSoup 0.9

Hi Ralph,

I was using TagSoup 0.8 with great success. On upgrading to 0.9 I have
this error:

TQ\TagSoup\TagSoupExtensions.lhs:29:17:

`Tag' is not applied to enough type arguments

Expected kind `*', but `Tag' has kind `* - *'

In the type synonym declaration for `Bundle'

Failed, modules loaded: TQ.Common.TextAndListHandling.

My change notes have this being a change between 0.6 and 0.8. As

Malcolm says, any old uses of Tag should become Tag String. The

reason is that Tag is now parameterised, and you can use Tag

ByteString etc. However, I should point out that Tag ByteString won't

be any faster than Tag String in this version (it's in the future work

pile).

Forgot to add: I now need to understand the following warnings on this

line import Text.HTML.Download:

Everyone's comments have been right. I previously included

Text.HTML.Download so that it was easy to test tagsoup against the

web. Since I first wrote that snippet the HTTP downloading libraries

have improved substantially, so people should use those in favour of

the version in tagsoup - you'll be able to connect to more websites in

more reliable ways, go through proxies etc. I don't intend to remove

the Download module any time soon, but I will do eventually.

Thanks, Neil
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] Re: currying combinators