- Haskell-Cafe - Haskell.org

Type family instances in Haddock?
by Sean Leather 30 Sep '11

30 Sep '11

Would it be useful/worthwhile to have type/data family instances show up in Haddock just as type class instances do? Regards, Sean

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Indentation problem using Happy
by Amy de Buitléir 30 Sep '11

30 Sep '11

I'm trying to use Happy for the first time, and I'm having trouble with this very simple example: ===== BEGIN: PolyParser.y ===== { module Main where import Char ( isAlpha, isDigit, isSpace ) } %name calc %tokentype { Token } %error { parseError } %token id { TokenId $$ } ',' { TokenCOMMA } wombat { TokenWombat $$ } %% Poly : id ',' wombat { parseError :: [Token] -> a parseError _ = error "Parse error" data Poly = Poly Int String deriving Show data Token = TokenId Int | TokenCOMMA | TokenWombat String deriving Show lexer :: String -> [Token] lexer [] = [] lexer (c:cs) | isSpace c = lexer cs | isAlpha c = lexVar (c:cs) | isDigit c = lexNum (c:cs) lexer (',':cs) = TokenCOMMA : lexer cs lexNum cs = TokenInt (read num) : lexer rest where (num,rest) = span isDigit cs lexVar cs = case span isAlpha cs of (wombat,rest) -> TokenWombat wombat : lexer rest (id,rest) -> TokenId id : lexer rest main = getContents >>= print . calc . lexer } ===== END: PolyParser.y ===== The resulting PolyParser.hs has an indentation problem (second-to-last line, below), so it won't compile. happyReduce_1 = happySpecReduce_3 4 happyReduction_1 happyReduction_1 _ _ _ = HappyAbsSyn4 (parseError :: [Token] -> a parseError _ = error "Parse error" Thank you in advance to anyone who can tell me where I've gone wrong.

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CFG specification and analysis directly in Haskell
by Anton Tayanovskyy 30 Sep '11

30 Sep '11

Hi, As a weekend hack, I just realized that Haskell has this wonderful DoRec syntax that among other things seems to be able to let the user express context-free grammars together with their processing rules in normal Haskell code, without template Haskell or anything like that, just like parser combinators. I am just wondering if this is this a known and useful result? Are there libraries doing similar stuff? I wrote up the Earley algorithm to demonstrate that one can in principle analyze the complete grammar (https://github.com/toyvo/haskell-earley) The result derivations `cheat` by using Data.Dynamic, but the result is quite pleasing, for example one can do: grammar :: G.Grammar (G.Rule Char E) grammar = do nat <- G.rule "NAT" [ fmap (\_ -> 0) (G.term '0') , fmap (\_ -> 1) (G.term '1') ] rec expr <- G.rule "EXPR" [ fmap Nat $ G.var nat , pure (\x _ y -> Add x y) <*> G.var expr <*> G.term '+' <*> G.var expr ] return expr Thanks, Anton

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Turn GC off
by Andreas Voellmy 30 Sep '11

30 Sep '11

Hi everyone, Is there a way to completely turn garbage collection off in the Haskell runtime system? I'm aware of the -A runtime option, but I'd like to completely turn it off, if possible. I'm OK with running the program until it runs out of memory, and I'm willing to recompile GHC if needed. Regards, Andreas

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Programming with arrows, exercises
by Sergey Mironov 30 Sep '11

30 Sep '11

Hello. I am reading "Programming with Arrows" by John Hughes (very helpful and interesting!), the book has an exercises requiring a module called Circuits for checking the answer. There should be things like class ArrowCircuit and various functions related to digital logic circuits simulation. Does anybody know where can I find one? Thanks, Sergey

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Cabal rebuilding of the C++ code for wxHaskell
by Dave Tapley 30 Sep '11

30 Sep '11

Hi all, I've been trying to resolve a compile time issue[1] with wxHaskell, and I thought I'd throw it open to see if anyone on cafe can help. Here's the crux of the issue: The Setup.hs for wxcore (the major component of wxHaskell) uses "simpleUserHooks", overriding only "confHook". However there is also "cleanHook", which is defined by simpleUserHooks to be: cleanHook = \p _ _ f -> clean p f, If you consult the source for clean[2] you'll see that it tries to "remove the whole dist/ directory rather than tracking exactly what files we created in there". I presume that's why we have to do a full re-build every time? To try and circumvent this I modified the definition of "main" in Setup.hs to this: main = defaultMainWithHooks simpleUserHooks { confHook = myConfHook, cleanHook = (\_ _ _ _ -> return ())} Unfortunately it still seems to re-build all the C++ on each 'install' from cabal. Not sure why? Dave, [1] http://sourceforge.net/mailarchive/message.php?msg_id=28099997 [2] Taken from http://www.haskell.org/ghc/docs/6.10.4/html/libraries/Cabal/src/Distributio… -- Cleaning clean :: PackageDescription -> CleanFlags -> IO () clean pkg_descr flags = do let distPref = fromFlag $ cleanDistPref flags notice verbosity "cleaning..." maybeConfig <- if fromFlag (cleanSaveConf flags) then maybeGetPersistBuildConfig distPref else return Nothing -- remove the whole dist/ directory rather than tracking exactly what files -- we created in there. chattyTry "removing dist/" $ do exists <- doesDirectoryExist distPref when exists (removeDirectoryRecursive distPref) -- these live in the top level dir so must be removed separately removeRegScripts -- Any extra files the user wants to remove mapM_ removeFileOrDirectory (extraTmpFiles pkg_descr) -- If the user wanted to save the config, write it back maybe (return ()) (writePersistBuildConfig distPref) maybeConfig where removeFileOrDirectory :: FilePath -> IO () removeFileOrDirectory fname = do isDir <- doesDirectoryExist fname isFile <- doesFileExist fname if isDir then removeDirectoryRecursive fname else if isFile then removeFile fname else return () verbosity = fromFlag (cleanVerbosity flags)

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HackageDB User Account
by Jonathan Frywater 30 Sep '11

30 Sep '11

How does one go about getting an account? I sent an email to the address provided at http://hackage.haskell.org/packages/accounts.html but haven't received any response yet. Since it's been over 3 weeks, I decided to try my luck here.

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LLVM: function pointer in global struct
by Tom Schouten 30 Sep '11

30 Sep '11

Hi everyone, Using the LLVM bindings, I'm trying to create an initialized global struct variable containing a pointer to a function. > {-# LANGUAGE ScopedTypeVariables #-} > import LLVM.Core > import Data.Word > import LLVM.Util.File(writeCodeGenModule) > sm_module = do > tick :: Function (Word32 -> IO Word32) <- createFunction ExternalLinkage $ \x -> ret x > info <- createNamedGlobal False ExternalLinkage "sm_info" $ constStruct (tick & ()) > return info I run into a complaint that this pointer isn't constant when it's part of a global variable initializer. No instance for (llvm-0.10.0.1:LLVM.Core.CodeGen.IsConstStruct (Function (Word32 -> IO Word32) :& ()) a0) arising from a use of `constStruct' Possible fix: add an instance declaration for (llvm-0.10.0.1:LLVM.Core.CodeGen.IsConstStruct (Function (Word32 -> IO Word32) :& ()) a0) In the second argument of `($)', namely `constStruct (tick & ())' In a stmt of a 'do' expression: info <- createNamedGlobal False ExternalLinkage "sm_info" $ constStruct (tick & ()) In a stmt of a 'do' expression: tick :: Function (Word32 -> IO Word32) <- createFunction ExternalLinkage $ \ x -> ret x I suppose this is because of > -- |A function is simply a pointer to the function. > type Function a = Value (Ptr a) being a Value instead of ConstValue. Is there a way around this? Cheers Tom

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PhD studentship in Nottingham
by Graham Hutton 29 Sep '11

29 Sep '11

Dear all, I am currently advertising a PhD Studentship in Functional Programming at the University of Nottingham in the UK: http://tinyurl.com/phd-nottingham Due to the nature of the funding, the position is only to UK/EU students who have resided in the UK for the last three years. If you are interested in applying yourself, please drop me a note by email. If you know of any good candidates who may be interested in applying, or there is a local mailing list for advertising such things, I'd be much obliged if you could pass on the above link. Many thanks, Graham Hutton -- Prof Graham Hutton Functional Programming Lab School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~gmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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network 2.3.05 on windows 7 with ghc-7.2.1
by Sai Hemanth K 29 Sep '11

29 Sep '11

Hi, Apologies if this is an off-topic for the list, If someone here managed to build network 2.3.05 on windows 7 with ghc-7.2.1 , could you kindly pass me the trick? The config step fails with missing header. I tried running it with mingw (tried with the latest one too - just in case : http://sourceforge.net/projects/mingw/files/Automated%20MinGW%20Installer/) I did not face any issue for the same thing on linux. Many thanks, Hemanth K

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