November 2010 - Haskell-Cafe

trouble with HDBC-mysql on Mac OS X
by Mark Lentczner 21 Nov '10

21 Nov '10

I'm having trouble with HDBC-mysql on Mac OS X (10.6, Snow Leopard). It compiles and builds fine, but when loaded (into ghci), the dynamic loader complains about not being able to find libmygcc.dylib. The issue is, MySQL's libmygcc is a static lib, not a dynamic one, so of course it won't find it. I've checked the build sequence that HDBC-mysql uses, and it calls upon mysql_config to generate the lib options. I've checked those and they are correct, expressly listing libmygcc statically (!). I've tried building against both the 64bit and 32bit versions of MySQL libs. (Suspect that only the 32bit should work.) Anyone have HDBC-mysql running on 10.6? Any ideas for me to try would be appreciated. - Mark Mark Lentczner http://www.ozonehouse.com/mark/ IRC: mtnviewmark

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ghc panic when compiling blaze-builder
by José Romildo Malaquias 21 Nov '10

21 Nov '10

When compiling blaze-builder-0.2.0.1 with ghc-7.0.1 on my ~amd64 gentoo system, I am getting the shown below. Any clues? Romildo [...] Building blaze-builder-0.2.0.1... [1 of 8] Compiling Blaze.ByteString.Builder.Internal ( Blaze/ByteString/Builder/Internal.hs, dist/build/Blaze/ByteString/Builder/Internal.o ) ghc: panic! (the 'impossible' happened) (GHC version 7.0.1 for x86_64-unknown-linux): dsLet: unlifted AbsBinds [b{tv aUH} [sk]] [] [pe{v axd} [lid] <= [b{tv aUH} [sk]] pe{v aUG} [lid]] pe{v axd} [lid] :: forall b{tv aUH} [sk]. base:GHC.Ptr.Ptr{tc 33A} b{tv aUH} [sk] [LclId] { {273:19-54} {273:19-54} !((pe{v aUG} [lid] :: base:GHC.Ptr.Ptr{tc 33A} b{tv aUH} [sk])) = {273:30-54} {273:33-41} (base:GHC.Ptr.plusPtr{v r4X} [gid]) @ base:GHC.Word.Word8{tc 32U} @ b{tv aUH} [sk] pf{v axc} [lid] firstBufSize{v arR} [lid] } EvBinds{{}} base:GHC.Base.>>={v 01P} [gid[ClassOp]] @ <nt>ghc-prim:GHC.Types.IO{tc 32I} $dMonad{v aUI} [lid] @ blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildSignal{tc rre} @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5} (step0{v arY} [lid] pf{v axc} [lid] (pe{v axd} [lid] @ base:GHC.Word.Word8{tc 32U})) (\ (next{v axT} [lid] :: blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildSignal{tc rre}) -> let { ds_d15b{v} [lid] :: blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildSignal{tc rre} [LclId] ds_d15b{v} [lid] = next{v axT} [lid] } in case ds_d15b{v} [lid] {ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}} of (wild_B1{v} [lid] :: blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildSignal{tc rre}) { blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.Done{d rrk} (rb_d15l{v} [lid] :: ghc-prim:GHC.Prim.Addr#{(w) tc 33}) -> let { pf'{v axU} [lid] :: base:GHC.Ptr.Ptr{tc 33A} base:GHC.Word.Word8{tc 32U} [LclId] pf'{v axU} [lid] = base:GHC.Ptr.Ptr{v rcP} [gid[DataCon]] @ base:GHC.Word.Word8{tc 32U} rb_d15l{v} [lid] } in let { fail_d15c{v} [lid] :: ghc-prim:GHC.Prim.State#{(w) tc 32q} ghc-prim:GHC.Prim.RealWorld{(w) tc 31E} -> ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5} [LclId] fail_d15c{v} [lid] = \ (ds_d15d{v} [lid] :: ghc-prim:GHC.Prim.State#{(w) tc 32q} ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}) -> base:GHC.Base.${v 019} [gid] @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5} @ (ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) (base:GHC.Base.return{v 01T} [gid[ClassOp]] @ <nt>ghc-prim:GHC.Types.IO{tc 32I} $dMonad{v aUN} [lid] @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) (bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.$WChunk{v reF} [gid[DataConWrapper]] (mkbs{v axe} [lid] @ base:GHC.Word.Word8{tc 32U} pf'{v axU} [lid]) k{v arT} [lid]) } in case base:GHC.Classes.=={v 01L} [gid[ClassOp]] @ (base:GHC.Ptr.Ptr{tc 33A} base:GHC.Word.Word8{tc 32U}) $dEq{v aUK} [lid] pf'{v axU} [lid] pf{v axc} [lid] {ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}} of (wild_B1{v} [lid] :: ghc-prim:GHC.Bool.Bool{(w) tc 3c}) { ghc-prim:GHC.Bool.False{(w) d 68} -> fail_d15c{v} [lid] ghc-prim:GHC.Prim.realWorld#{(w) v 0o} [gid]; ghc-prim:GHC.Bool.True{(w) d 6u} -> base:GHC.Base.return{v 01T} [gid[ClassOp]] @ <nt>ghc-prim:GHC.Types.IO{tc 32I} $dMonad{v aUL} [lid] @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5} k{v arT} [lid] }; blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BufferFull{d rri} (rb_d15n{v} [lid] :: ghc-prim:GHC.Prim.Int#{(w) tc 3G}) (rb_d15o{v} [lid] :: ghc-prim:GHC.Prim.Addr#{(w) tc 33}) (nextStep{v axX} [lid] :: blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildStep{tc rrc}) -> let { newSize{v axV} [lid] :: ghc-prim:GHC.Types.Int{(w) tc 3J} [LclId] newSize{v axV} [lid] = ghc-prim:GHC.Types.I#{(w) v 6d} [gid[DataCon]] rb_d15n{v} [lid] } in let { pf'{v axW} [lid] :: base:GHC.Ptr.Ptr{tc 33A} base:GHC.Word.Word8{tc 32U} [LclId] pf'{v axW} [lid] = base:GHC.Ptr.Ptr{v rcP} [gid[DataCon]] @ base:GHC.Word.Word8{tc 32U} rb_d15o{v} [lid] } in let { l{v aUP} [lid] :: ghc-prim:GHC.Types.Int{(w) tc 3J} [LclId] l{v aUP} [lid] = base:GHC.Ptr.minusPtr{v r4U} [gid] @ base:GHC.Word.Word8{tc 32U} @ base:GHC.Word.Word8{tc 32U} pf'{v axW} [lid] pf{v axc} [lid] } in case l{v aUP} [lid] {ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}} of (l{v aUP} [lid] :: ghc-prim:GHC.Types.Int{(w) tc 3J}) { __DEFAULT -> let { l{v axY} [lid] :: ghc-prim:GHC.Types.Int{(w) tc 3J} [LclId] l{v axY} [lid] = l{v aUP} [lid] } in base:GHC.Base.${v 019} [gid] @ blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildStep{tc rrc} @ (ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) (fillNewBuffer{v arW} [lid] (base:GHC.Classes.max{v rG} [gid[ClassOp]] @ ghc-prim:GHC.Types.Int{(w) tc 3J} $dOrd{v aUQ} [lid] (base:GHC.Num.+{v r24} [gid[ClassOp]] @ ghc-prim:GHC.Types.Int{(w) tc 3J} $dNum{v aY6} [lid] l{v axY} [lid] newSize{v axV} [lid]) minBufSize{v arQ} [lid])) (\ (pfNew{v axZ} [lid] :: base:GHC.Ptr.Ptr{tc 33A} base:GHC.Word.Word8{tc 32U}) (peNew{v ay0} [lid] :: base:GHC.Ptr.Ptr{tc 33A} base:GHC.Word.Word8{tc 32U}) -> base:GHC.Base.>>{v 01Q} [gid[ClassOp]] @ <nt>ghc-prim:GHC.Types.IO{tc 32I} $dMonad{v aY7} [lid] @ ghc-prim:GHC.Unit.(){(w) tc 40} @ blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildSignal{tc rre} (base:Foreign.Marshal.Utils.copyBytes{v r4c} [gid] @ base:GHC.Word.Word8{tc 32U} pfNew{v axZ} [lid] pf{v axc} [lid] l{v axY} [lid]) (nextStep{v axX} [lid] (base:GHC.Ptr.plusPtr{v r4X} [gid] @ base:GHC.Word.Word8{tc 32U} @ base:GHC.Word.Word8{tc 32U} pfNew{v axZ} [lid] l{v axY} [lid]) peNew{v ay0} [lid])) }; blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.ModifyChunks{d rrg} (rb_d15q{v} [lid] :: ghc-prim:GHC.Prim.Addr#{(w) tc 33}) (bsk{v ay2} [lid] :: bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5} -> bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) (nextStep{v ay3} [lid] :: blaze-builder-0.2.0.1:Blaze.ByteString.Builder.Internal.BuildStep{tc rrc}) -> let { pf'{v ay1} [lid] :: base:GHC.Ptr.Ptr{tc 33A} base:GHC.Word.Word8{tc 32U} [LclId] pf'{v ay1} [lid] = base:GHC.Ptr.Ptr{v rcP} [gid[DataCon]] @ base:GHC.Word.Word8{tc 32U} rb_d15q{v} [lid] } in let { fail_d15g{v} [lid] :: ghc-prim:GHC.Prim.State#{(w) tc 32q} ghc-prim:GHC.Prim.RealWorld{(w) tc 31E} -> ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5} [LclId] fail_d15g{v} [lid] = \ (ds_d15h{v} [lid] :: ghc-prim:GHC.Prim.State#{(w) tc 32q} ghc-prim:GHC.Prim.RealWorld{(w) tc 31E}) -> base:GHC.Base.${v 019} [gid] @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5} @ (ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) (base:GHC.Base.return{v 01T} [gid[ClassOp]] @ <nt>ghc-prim:GHC.Types.IO{tc 32I} $dMonad{v aYc} [lid] @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) (bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.$WChunk{v reF} [gid[DataConWrapper]] (mkbs{v axe} [lid] @ base:GHC.Word.Word8{tc 32U} pf'{v ay1} [lid]) (bsk{v ay2} [lid] (base:GHC.Base.${v 019} [gid] @ (ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5} (bytestring-0.9.1.8:Data.ByteString.Internal.inlinePerformIO{v riV} [gid] @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) (fillNewBuffer{v arW} [lid] bufSize{v arP} [lid] nextStep{v ay3} [lid])))) } in case base:GHC.Classes.=={v 01L} [gid[ClassOp]] @ (base:GHC.Ptr.Ptr{tc 33A} base:GHC.Word.Word8{tc 32U}) $dEq{v aY9} [lid] pf'{v ay1} [lid] pf{v axc} [lid] {ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}} of (wild_B1{v} [lid] :: ghc-prim:GHC.Bool.Bool{(w) tc 3c}) { ghc-prim:GHC.Bool.False{(w) d 68} -> fail_d15g{v} [lid] ghc-prim:GHC.Prim.realWorld#{(w) v 0o} [gid]; ghc-prim:GHC.Bool.True{(w) d 6u} -> base:GHC.Base.${v 019} [gid] @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5} @ (ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) (base:GHC.Base.return{v 01T} [gid[ClassOp]] @ <nt>ghc-prim:GHC.Types.IO{tc 32I} $dMonad{v aYa} [lid] @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) (bsk{v ay2} [lid] (base:GHC.Base.${v 019} [gid] @ (ghc-prim:GHC.Types.IO{tc 32I} bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5} (bytestring-0.9.1.8:Data.ByteString.Internal.inlinePerformIO{v riV} [gid] @ bytestring-0.9.1.8:Data.ByteString.Lazy.Internal.ByteString{tc rg5}) (fillNewBuffer{v arW} [lid] bufSize{v arP} [lid] nextStep{v ay3} [lid]))) } })

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Interactive OpenGL-based graphics and ghci?
by Conal Elliott 20 Nov '10

20 Nov '10

I'm trying to find some way to do interactive, OpenGL-based graphics in Haskell on Mac OS X. Does anyone here use GLUT or SDL on Mac OS X with ghci, or maybe an alternative library? Using ghci is very important to me, as my programs are pretty high-level and are often half-liners. I'm using gtk2hs for now, but I want something that works more natively, i.e., without the awkwardness of going through the X server. Thanks, - Conal

3 2

Downloading web page in Haskell
by José Romildo Malaquias 20 Nov '10

20 Nov '10

In order to download a given web page, I wrote the attached program. The problem is that the page is not being full downloaded. It is being somehow intettupted. Any clues on how to solve this problem? Romildo

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category-extras clash with transformers
by Tony Morris 20 Nov '10

20 Nov '10

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I have installed mtl-1.1.1.0 so that xmonad-contrib-0.9.1 would compile with GHC 6.12.1. http://permalink.gmane.org/gmane.comp.lang.haskell.xmonad/10603 Then I tried to installed category-extras-0.53.5, which clashed with transformers-0.2.2.0 for the Applicative/Monad instances for Either. Is there any way out of this problem? Thanks for any pointers. $ ghc-pkg list | grep mtl mtl-1.1.1.0 mtl-2.0.1.0 $ ghc-pkg list | grep transformers transformers-0.2.2.0 $ cabal install category-extras ... [39 of 99] Compiling Control.Monad.Either ( src/Control/Monad/Either.hs, dist/build/Control/Monad/Either.o ) src/Control/Monad/Either.hs:44:9: Duplicate instance declarations: instance Monad (Either e) -- Defined at src/Control/Monad/Either.hs:44:9-24 instance Monad (Either e) -- Defined in transformers-0.2.2.0:Control.Monad.Trans.Error src/Control/Monad/Either.hs:49:9: Duplicate instance declarations: instance Applicative (Either e) -- Defined at src/Control/Monad/Either.hs:49:9-30 instance Applicative (Either e) -- Defined in transformers-0.2.2.0:Control.Monad.Trans.Error src/Control/Monad/Either.hs:53:9: Duplicate instance declarations: instance MonadFix (Either e) -- Defined at src/Control/Monad/Either.hs:53:9-27 instance MonadFix (Either e) -- Defined in transformers-0.2.2.0:Control.Monad.Trans.Error cabal: Error: some packages failed to install: category-extras-0.53.5 failed during the building phase. The exception was: ExitFailure 1 - -- Tony Morris http://tmorris.net/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkznxgQACgkQmnpgrYe6r60dkACfZQkYKbMOQuGfaVpFb2MfhJWD asAAn1/hoX+m/YpUOch3r4NsR99y2htz =IsZc -----END PGP SIGNATURE-----

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RegEx versus (Parsec, TagSoup, others...)
by Michael Litchard 20 Nov '10

20 Nov '10

I've been working on a project that requires me to do screen scraping. When I first started this, I worked off of other people's examples. Not one used regex. By luck I found someone at work to help me along this project. His clues and hints don't use regex either. I was at a point where I had to make a decision concerning design, so I asked the guy sitting next to me at work. He's very experienced, and comes from a Perl perspective. I let him into what I was doing, and he opined I should be using pcre. So now I'm second guessing my choices. Why do people choose not to use regex for uri parsing?

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Re: [Haskell-cafe] Quasi quotation question
by Oscar Finnsson 20 Nov '10

20 Nov '10

Sure. Just use http://hackage.haskell.org/package/haskell-src-meta-0.0.6. You are probably interested in parsePat or parseExp. I've used parseExp in a package. -- Oscar

1 0

Quasi quotation question
by jean-christophe mincke 19 Nov '10

19 Nov '10

Hello, Is it possible for a quasi quoter to have access to information about haskell identifiers declared before the quasi-quotation? I tried the 'reify' function but without success. Just as in the following exemple: a = 6 x = [$expr|a|] Where the generated haskell code is a= 6 x = a Thank you Regards J-C

2 1

GitIt
by Andrew Coppin 19 Nov '10

19 Nov '10

The other day, I did a slightly foolish thing. I uttered the command cabal install gitit Actually, while I was "foolish", it actually worked better than you'd think. It wanted to install several thousand billion packages, but all of them compiled without issue. Well, all except one. You see, for reasons that I have yet to determine, cabal is *convinced* that gitit transitively requires the "unix" package. Astonishingly, this doesn't work on Windows. :-P Question: Why does 90% of the network-related stuff on Hackage require the unix package? What's in there that's so network-related? I don't understand. We've *got* a portable "network" package that works on all platforms, so...? Anyway, on further investigation, it appears that the culprit is "cautious-file". If a certain CPP flag it set, "unix" gets added to the Build-Depends: field. Except... I didn't set any CPP flags! What the hell? So I manually edit the package description (!), and now it builds and installs perfectly happily. So now I tell cabal to install gitit again... and it immediately tries to install unix, even though the only package that (it thinks) requires unix is already installed? Wuh? So I unpack gitit and tell cabal to build it. Building takes about 30 seconds. *Linking* takes about 4 minutes (??!) And then it fails due to some missing symbols. (No, I don't remember off the top of my head what they were.) At this point, I am completely lost. Does anybody have any ideas on how I can make GitIt work, short of installing Linux? I've searched and searched and I can't see a pre-built binary anywhere.

2 2

Impredicative Types
by Gregory Crosswhite 19 Nov '10

19 Nov '10

Hey everyone! I haven't had a chance to try out GHC 7 myself, but I saw in the documentation that Impredicative Types are still supported. Is this true? I thought that they were on their way out because they overcomplicated type checking; has this plan been changed? Cheers, Greg

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