July 2010 - Haskell-Cafe

HTTP Redirect With HTTPS Rejected
by aditya siram 20 Jul '10

20 Jul '10

The problem is that any page that that responds with 301.302,303 or 307 and redirects to an "https" is rejected by the library. The code that does the rejection is in "Network.Browser" on line 865. It only accepts "http:". Why was this design decision made? It makes it impossible for me to use this library for my project. -deech On Tue, Jul 20, 2010 at 3:30 PM, aditya siram <aditya.siram(a)gmail.com> wrote: > Hi all, > I am trying to simply download a web page using the HTTP library. It > works fine with "http://www.google.com" but a redirecting page like > "http://gmail.com" creates an error. Code is at > http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27864#a27864. > > Thanks , > -deech >

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Regex multiple matches
by Omari Norman 20 Jul '10

20 Jul '10

Hi, How do I use Text.Regex.PCRE to get information on multiple matches? For instance, in ghci I get this error message: Prelude Text.Regex.PCRE> "foo" =~ "o" :: [(Int,Int)] <interactive>:1:0: No instance for (RegexContext Regex [Char] [(Int, Int)]) arising from a use of `=~' at <interactive>:1:0-11 Possible fix: add an instance declaration for (RegexContext Regex [Char] [(Int, Int)]) In the expression: "foo" =~ "o" :: [(Int, Int)] In the definition of `it': it = "foo" =~ "o" :: [(Int, Int)] "Real World Haskell"'s text suggests this should work, but the ghci output is littered with errors. http://book.realworldhaskell.org/read/efficient-file-processing-regular-exp… Thanks for any help. Omari

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HTTP Redirect Error
by aditya siram 20 Jul '10

20 Jul '10

Hi all, I am trying to simply download a web page using the HTTP library. It works fine with "http://www.google.com" but a redirecting page like "http://gmail.com" creates an error. Code is at http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27864#a27864. Thanks , -deech

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seeking guideline re modules and stacks of State Monad Transformers
by Ali Razavi 20 Jul '10

20 Jul '10

Hi, I am working on a project that features a few modules with inter-dependent states. It is expected that some of the modules import and use some of the stateful functions from other modules, and simultaneously, need to manage the state of their own. I need to make a design choice as to whether I should add the new modules' state as separate layesr by transforming the monad transformer stack in each module, or create a separate module to handle the amalgamation of all states with a single datatype. Both solutions have salient issues. The latter, namely stacking more layers, can quickly become unwieldy, whereas the former breaches encapsulation. Any better ideas? To give it more of a concrete context, imagine the following: module A where type AState = State Int.... someAFunc :: a -> AState a --------------- module B where type BState = StateT Int AState ... someBFunc :: b -> BState b -------------- -- now I want module C to only have access to B's part of BState, but not the A-related part module C where type CState = StateT Int BState Thanks, Ali

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Talking to Java from Haskell?
by Daniel Cook 20 Jul '10

20 Jul '10

Hi, Someone has written a large Java library (QuickFIX/J) which speaks a gnarled, ugly protocol (FIX). There don't appear to be any FIX protocol libraries in Hackage. I need my Haskell program to talk to a 3rd-party system that only speaks FIX. Should I: a) Reimplement the protocol directly Haskell? (This appears to be non-trivial) b) Wrap the Java library with some code to use a lightweight message queue (zeromq) to send messages to my Haskell program? (This would require essentially re-implementing an abstracted subset of the the protocol into 0MQ messages) c) Find a way for Haskell to interact directly with Java? (the various JNI bridges seem very unmaintained...) To me, (b) seems like the best approach, but I'd like to hear what the cafe thinks.. Cheers, - Dan

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Re: [Haskell] ANNOUNCE: Haskell 2010 Report (final)
by Roman Cheplyaka 20 Jul '10

20 Jul '10

* Simon Marlow <marlowsd(a)gmail.com> [2010-07-06 13:00:36+0100] > The Haskell 2010 report is done! I've uploaded it to > www.haskell.org, and linked it from the main Haskell wiki: > > http://www.haskell.org/haskellwiki/Language_and_library_specification > > online HTML version: > > http://www.haskell.org/onlinereport/haskell2010 > > PDF: > > http://www.haskell.org/definition/haskell2010.pdf Greetings! Now, can different compiler/interpreter authors make statements about support of this standard in their compilers please? -- Roman I. Cheplyaka :: http://ro-che.info/ "Don't let school get in the way of your education." - Mark Twain

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Design for 2010.2.x series Haskell Platform site
by Don Stewart 20 Jul '10

20 Jul '10

Hey all, As you might know, the next major release of the Haskell Platform is coming up next week. We've had the current download site design for a while now: http://haskell.org/platform/ However, I'm thinking it would be nice to have themed release designs. Examples: http://www.gnome.org/ GNOME 2.30 Ubuntu, http://www.ubuntu.com/ and so on. If anyone is interested in a 2010.2 series design for the HP site, the repository containing the stylesheet is here: http://code.haskell.org/haskell-platform/ And you can find the index.html and style.css in the download-website/ directory. We worked faily hard on the content, but feel free to play with the style. -- Don

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ANNOUNCE: AngloHaskell 2010 - CALL FOR TALKS
by Derek Wright 20 Jul '10

20 Jul '10

AngloHaskell 2010 - ANNOUNCEMENT and CALL FOR TALKS AngloHaskell 2010 - 5th Annual Haskell Meeting in England Friday September 10th and Saturday September 11th, 2010 Microsoft Research, Cambridge, UK http://www.haskell.org/haskellwiki/AngloHaskell/2010 [Please note the change of date from previous years and earlier discussions] AngloHaskell is a free gathering of all people Haskell-related from beginners to seasoned hackers, both academic and industrial. AngloHaskell 2010 is generously hosted by Microsoft Research. As a result no charge is made for attending or speaking. Friday will be a day of talks and discussion at MSR followed by a more informal day of activities on Saturday somewhere else in Cambridge. AngloHaskell welcomes talks on all Haskell related subjects. From short comments (Functional Grit) to full presentations, all are welcome. Please add your name and the title of your talk to the wiki page (or email me and I will add it for you). If you want to attend (even if you are only a possible at the moment) please add your name to the wiki page, or let me know by email. Organisational discussions are on held on the #anglohaskell channel on the Freenode IRC network, feel free to drop in with questions or comments.

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Re: [Haskell-cafe] Tiger compiler in Haskell: annotating abstract syntax tree
by Job Vranish 19 Jul '10

19 Jul '10

Ah, I found the attachment on your other email. I would recommend using the Fix and Ann types, instead of the AnnFix type. I modified your code a bit (and fixed the Show instances etc...) and put it here: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27823#a27823 Let me know if you have questions about it. - Job <http://hpaste.org/fastcgi/hpaste.fcgi/view?id=27823#a27823> 2010/7/19 Job Vranish <job.vranish(a)gmail.com> > I didn't get any attachments from you, but haskell-cafe might filter them > out (I'm not sure). > > But, the usual derived instances for Show should work fine for your > expression and annotation types. > For the Fix type you can use: > > instance (Show (f (Fix f))) => Show (Fix f) where > show (Fix a) = show "Fix " ++ show a > > hmmm, but you'll probably need: > > {-# LANGUAGE FlexibleContexts, UndecidableInstances #-} > > > - Job > > > > 2010/7/19 José Romildo Malaquias <j.romildo(a)gmail.com> > >> On Mon, Jul 19, 2010 at 01:51:57PM -0400, Job Vranish wrote: >> > Martijn van Steenbergen has a good blog post that describes the method I >> > generally use: >> > >> http://martijn.van.steenbergen.nl/journal/2010/06/24/generically-adding-pos… >> > >> > In his example he annotates the expression tree with position >> information, >> > but you can use the same method to add type annotations, or whatever you >> > want. >> >> After a quick read at Martijn blog article I've written the attached >> test program, which works. >> >> But I am not succeeding in deriving Show for the data types. Any help? >> >> Romildo >> >> > 2010/7/19 José Romildo Malaquias <j.romildo(a)gmail.com> >> > >> > > Hello. >> > > >> > > In his book "Modern Compilder Implementation in ML", Appel presents a >> > > compiler project for the Tiger programming language where type >> checking >> > > and intermediate code generation are intrinsically coupled. >> > > >> > > There is a function >> > > >> > > transExp :: Absyn.Exp -> (Tree.Exp,Types.Type) >> > > >> > > that do semantic analysis, translating an expression to the Tree >> > > intermediate representation language and also do type checking, >> > > calculating the type of the expression. >> > > >> > > Maybe the compiler can be made more didatic if these phases are >> separate >> > > phases of compilation. >> > > >> > > The type checker would annotate the abstract syntax tree (ast) with >> type >> > > annotations, that could be used later by the translater to >> intermediate >> > > representation. >> > > >> > > In an imperative language probably each relevant ast node would have a >> > > field for the type annotation, and the type checker would assign the >> > > type of the node to this field after computing it. >> > > >> > > I am writing here to ask suggestions on how to annotate an ast with >> > > types (or any other information that would be relevant in a compiler >> > > phase) in Haskell. >> > > >> > > As an example, consider the simplified ast types: >> > > >> > > data Exp >> > > = IntExp Integer >> > > | VarExp Symbol >> > > | AssignExp Symbol Exp >> > > | IfExp Exp Exp (Maybe Exp) >> > > | CallExp Symbol [Exp] >> > > | LetExp [Dec] Exp >> > > >> > > data Dec >> > > = TypeDec Symbol Ty >> > > | FunctionDec Symbol [(Symbol,Symbol)] (Mybe Symbol) Exp >> > > | VarDec Symbol (Maybe Symbol) Exp >> > > >> > > Expressions can have type annotations, but declarations can not. >> > > >> > > Comments? >> > >

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RE: Design for 2010.2.x series Haskell Platform site (Don Stewart)
by Niemeijer, R.A. 19 Jul '10

19 Jul '10

> Is it just me, or does aligning [OSX,Win,Linux] `zip` [Comprehensive, > Robust, CuttingEdge] send the wrong message... Yeah, I noticed that too when designing it, but at the time it didn't bother me too much. I do see how it could confuse some people though, so I've made a design alternative that solves this problem. I think it also makes for a better landing page for people who don't yet know anything about Haskell, since the current design doesn't explain what Haskell actually is. I'll let you guys be the judge though. New alternative: http://dl.dropbox.com/u/623671/haskell_platform_redesign/index2.htm

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