August 2011 - Haskell-Cafe

Re: [Haskell-cafe] Project Euler: request for comments
by KC 26 Aug '11

26 Aug '11

Is Problem 11 the 4 consecutive #'s problem? If so what must be true for 4 #'s to have a large product? Hint: x * y * z * 2 is that going to be larger? -- -- Regards, KC

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Dynamic loading of module
by Arnaud Bailly 26 Aug '11

26 Aug '11

Hello, I stumbled upon this blog post describing a method from dynamically loading modules using GHC api. While trying to test the given method, I got the following error which obviously tells me my packages are not correctly installed but I have no idea how to fix this. D:\projets\>ghc -package ghc main.hs --make <command line>: cannot satisfy -package ghc: ghc-7.0.3-fc75cf67c86ba2c0d64b07024a18d3b4 is unusable due to missing or recursive dependencies: template-haskell-2.5.0.0-7d9b1443ac5ab69e5ed705a487990deb (use -v for more information) When I run ghc-pkg check, I got which obviously is bad. There are problems in package test-framework-0.3.3: dependency "regex-posix-0.94.4-7963833a181f95ba404a78e3e76d835a" doesn't exist There are problems in package QuickCheck-2.4.0.1: dependency "template-haskell-2.5.0.0-e5fd973432385747440288b48f6a6a5a" doesn't exist There are problems in package snap-0.5.1: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package snap-server-0.5.1: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "attoparsec-enumerator-0.2.0.3-d5a7e5b640b4b27be4c6d0c9a314dd0a" doesn't exist dependency "binary-0.5.0.2-72c84eaab351d41e936261d8d5d416f5" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package snap-core-0.5.1: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "attoparsec-enumerator-0.2.0.3-d5a7e5b640b4b27be4c6d0c9a314dd0a" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package heist-0.5.2: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package xmlhtml-0.1.5: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package authenticate-0.9.0.1: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package http-enumerator-0.6.5.1: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "attoparsec-enumerator-0.2.0.3-d5a7e5b640b4b27be4c6d0c9a314dd0a" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package zlib-enum-0.2.1: dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package yesod-static-0.1.0: dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "pureMD5-2.1.0.3-cb7a7a936930b56c62f9207838b99efb" doesn't exist There are problems in package yesod-form-0.1.0.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "data-default-0.2.0.1-14197e607852c0357951d749c098bd34" doesn't exist There are problems in package yesod-core-0.8.2: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package warp-0.4.0.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package wai-extra-0.4.0.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package wai-app-static-0.1.0: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package wai-0.4.0: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package hjsmin-0.0.14: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package aeson-0.3.2.6: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package tls-extra-0.2.3: dependency "crypto-api-0.6.1-6854b68ffc32d8880becebcf8b612932" doesn't exist There are problems in package tls-0.6.4: dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "crypto-api-0.6.1-6854b68ffc32d8880becebcf8b612932" doesn't exist There are problems in package cprng-aes-0.2.1: dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "crypto-api-0.6.1-6854b68ffc32d8880becebcf8b612932" doesn't exist There are problems in package cryptocipher-0.2.12: dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "crypto-api-0.6.1-6854b68ffc32d8880becebcf8b612932" doesn't exist dependency "tagged-0.2.2-74797b2dae44925f852c0beab1f9f3e6" doesn't exist There are problems in package blaze-textual-0.1.0.0: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package SHA-1.4.1.3: dependency "binary-0.5.0.2-72c84eaab351d41e936261d8d5d416f5" doesn't exist There are problems in package RSA-1.0.6.1: dependency "binary-0.5.0.2-72c84eaab351d41e936261d8d5d416f5" doesn't exist dependency "pureMD5-2.1.0.3-cb7a7a936930b56c62f9207838b99efb" doesn't exist There are problems in package persistent-0.5.0: dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package mime-mail-0.3.0: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package hxt-9.1.1: dependency "binary-0.5.0.2-72c84eaab351d41e936261d8d5d416f5" doesn't exist There are problems in package http-types-0.6.4: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist There are problems in package hamlet-0.8.2: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package cryptohash-0.7.0: dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "crypto-api-0.6.1-6854b68ffc32d8880becebcf8b612932" doesn't exist dependency "tagged-0.2.2-74797b2dae44925f852c0beab1f9f3e6" doesn't exist There are problems in package cookie-0.2.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package blaze-html-0.4.1.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package blaze-builder-enumerator-0.2.0.2: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package attoparsec-text-0.8.5.0: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist There are problems in package asn1-data-0.5.0: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "attoparsec-enumerator-0.2.0.3-d5a7e5b640b4b27be4c6d0c9a314dd0a" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist The following packages are broken, either because they have a problem listed above, or because they depend on a broken package. test-framework-0.3.3 QuickCheck-2.4.0.1 snap-0.5.1 snap-server-0.5.1 snap-core-0.5.1 heist-0.5.2 xmlhtml-0.1.5 authenticate-0.9.0.1 http-enumerator-0.6.5.1 zlib-enum-0.2.1 yesod-static-0.1.0 yesod-form-0.1.0.1 yesod-core-0.8.2 warp-0.4.0.1 wai-extra-0.4.0.1 wai-app-static-0.1.0 wai-0.4.0 hjsmin-0.0.14 aeson-0.3.2.6 tls-extra-0.2.3 tls-0.6.4 cprng-aes-0.2.1 cryptocipher-0.2.12 blaze-textual-0.1.0.0 SHA-1.4.1.3 RSA-1.0.6.1 persistent-0.5.0 mime-mail-0.3.0 hxt-9.1.1 http-types-0.6.4 hamlet-0.8.2 cryptohash-0.7.0 cookie-0.2.1 blaze-html-0.4.1.1 blaze-builder-enumerator-0.2.0.2 attoparsec-text-0.8.5.0 asn1-data-0.5.0 test-framework-quickcheck2-0.2.10 test-framework-hunit-0.2.6 yesod-persistent-0.1.0 yesod-json-0.1.1 persistent-template-0.5.0.1 certificate-0.9.0.1 haskell-platform-2011.2.0.1 Is there anything I can do to fix this without wiping out and reinstalling haskell platform ? THanks in advance Arnaud

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RFC: decodeFloat
by Daniel Fischer 26 Aug '11

26 Aug '11

Occasionally, the behaviour of decodeFloat and its consequences causes concern and/or bug reports (e.g. http://hackage.haskell.org/trac/ghc/ticket/3898) The main problem is the treatment of NaNs and infinities (that it doesn't distinguish between 0.0 and -0.0 is a minor thing), which are converted as if they were ordinary finite values. Thus, for example, decodeFloat (1/0 :: Double) = (2^52,972) and consequently floor (1/0 :: Double) = 2^1024 (corresponding for round, truncate, ceiling, properFraction), significand (1/0 :: Double) = 0.5, Prelude> uncurry encodeFloat (decodeFloat (1/0 :: Float)) :: Double 3.402823669209385e38 and similar meaningless/nonsensical results for NaNs. At its type, decodeFloat :: RealFloat a => a -> (Integer, Int), I see only two reasonable options, 1. leave the behaviour as it is, just warn about the exceptional cases in the documentation, 2. let decodeFloat raise an error when its argument is a NaN or infinite. Both options have disadvantages, 1. makes it easy to get meaningless results when there's a non-finite value around, 2. incurs a nontrivial performance penalty. Paying that performance penalty when dealing only with known-to-be-good values is undesirable, but so are meaningless results. A third option would be providing both behaviours by adding a function. That could take several forms, a) leave decodeFloat as is and add safeDecodeFloat outside the RealFloat class, that would check the value first and then either raise an error on NaN/Infinity or return a Maybe (Integer, Int), b) add a function to the RealFloat class, either leave decodeFloat as is and add safeDecodeFloat with the behaviour as in a) or change decodeFloat according to 2. and add unsafeDecodeFloat with the current behaviour. The drawback of a) is that safeDecodeFloat would have to perform two checks, while with IEEE Doubles/Floats, the result could be determined by one check (which would also be simpler than each of isNaN and isInfinite). Also, which module should export it? The drawback of b) is adding a function to RealFloat, as if that wasn't big enough already. Since both behaviours allow a default definition in terms of the other, only code that by chance uses the new name would break. What would be the community's preferred way to handle this issue? Cheers, Daniel

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Make shared library - questions
by Sergiy Nazarenko 26 Aug '11

26 Aug '11

Hi ! I'm trying to compile shared library. This library will use as part of plugin for some program. If I compile library with option -dynamic my library has links for HS libraries like libHSbase-4.2.0.2-ghc6.12.3.so and so on. But program has crashed constantly. Is it possible to make shared library without -dynamic flag? I want to try to make library without dependencies. According to http://www.well-typed.com/blog/30 theoretically I can do this but I found this impossible - http://hackage.haskell.org/trac/ghc/ticket/3704 My options to compile: ghc -O2 --make -no-hs-main -dynamic -shared -fPIC -optl '-shared' -optc '-DMODULE=MyLib' -o MyLib.so MyLib.hs module_init.c -optl-Wl -lHSrts-ghc6.12.3 If I try compile without -dynamic I get error: /usr/bin/ld: /usr/local/lib/ghc-6.12.3/base-4.2.0.2/libHSbase-4.2.0.2.a(Conc__270.o): relocation R_X86_64_32 against `base_GHCziConc_ensureIOManagerIsRunning1_closure' can not be used when making a shared object; recompile with -fPIC /usr/local/lib/ghc-6.12.3/base-4.2.0.2/libHSbase-4.2.0.2.a: could not read symbols: Bad value collect2: ld returned 1 exit status My system is: Cenos 5.6 ghc6.12.3 gcc-4.2.1 Cheers, Sergiy

2 1

a minor bug (memory leak) in ListLike package
by bob zhang 26 Aug '11

26 Aug '11

Hi, John, there is a space leak problem in ListLike typeclass, in the method genericLength calclen !accum cl = calclen accum cl = --- thank you for your nice library btw, is there any way to derive ListLike interface automatically? for such type : newtype List a = List {[a]} Best,bob

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hoogle data no connection to host http://code.galois.com/darcs/haskell-platform ...
by informationen 26 Aug '11

26 Aug '11

Hi, i installed Hoogle succesfullly with cabal install hoogle then i try to run hoogle data but the connection to http://code.galois.com/darcs/haskell-platform/haskell-platform.cabal times out. How can i download the data needed for the hoogle command line tool? Greetings Chris

2 1

ANN: shelltestrunner 1.1
by Simon Michael 26 Aug '11

26 Aug '11

I'm pleased to announce shelltestrunner 1.1. shelltestrunner tests command-line programs or arbitrary shell commands. It reads simple declarative tests specifying a command, some input, and the expected output, error output and exit status. Tests can be run selectively, in parallel, with a timeout, in color, and/or with differences highlighted. Projects using it include hledger, yesod, and berp. shelltestrunner is free software released under GPLv3+. New in 1.1: * bump process dependency to allow building with GHC 7.2.1 * new `-a/--all` flag shows all failure output without truncating Home page: http://joyful.com/shelltestrunner Install: $ cabal install shelltestrunner

2 1

ping haskell.org timeout
by Greg Fitzgerald 26 Aug '11

26 Aug '11

"cabal update" hangs. "ping haskell.org" times out. But haskell.org and hackage webpages are loading just fine. What's going on? Thanks, Greg

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Cabal-1.10.1.0 and bytestring-0.9.2.0 hackage problem.
by Bertram Felgenhauer 25 Aug '11

25 Aug '11

Dear list, Cabal-1.10.1.0 contains a bug that causes it to fail to parse the test-suite target of bytestring-0.9.2.0. Since cabal-install parses all package descriptions to before resolving dependencies, users with that version of Cabal are stuck. Now it seems somebody realised this problem and removed bytestring-0.9.2.0 from hackage. However, 1. http://hackage.haskell.org/package/bytestring is now broken. 2. The downloadeble package index (00-index.tar) still contains the bytestring-0.9.2.0 cabal file, so the problem persists. As a workaround, one can remove the cabal file from the downloaded index manually, tar -f ~/.cabal/packages/hackage.haskell.org/00-index.tar --delete bytestring/0.9.2.0 (or rebuild Cabal / cabal-install starting with 'cabal unpack Cabal; cabal unpack cabal-install') But it really needs to be fixed on the hackage server. Best regards, Bertram

3 2

do-re-mi
by Albert Y. C. Lai 25 Aug '11

25 Aug '11

do, a block, a monad block rec, a knot tied in the block mu, a name that calls itself (mu is pronounced as me in modern Greek) forM_, a long long list to run SO, a state aborting threads (SO is stack overflow) la, a state to follow SO T's, tranformers of monads that will bring us back to do

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