- Haskell-Cafe - Haskell.org

haskell-src-exts should depend on happy
by Ozgur Akgun 28 Aug '11

28 Aug '11

Hi, cabal installing haskell-src-exts fails, because of an unlisted dependency to the happy executable. The following succeeds: cabal install happy; cabal install haskell-src-exts Thanks, Ozgur

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Class instances in haddock documentation missing
by Joachim Breitner 28 Aug '11

28 Aug '11

Hi, the haddock information generated on hackage lists class instances per class and per data type e.g. on http://hackage.haskell.org/packages/archive/base/4.3.1.0/doc/html/Data-Eq.h… or http://hackage.haskell.org/packages/archive/xhtml/3000.2.0.1/doc/html/Text-… For some reason, the documentation generated on Debian does not. Does anybody have an idea why that could be? We use ./Setup haddock --hyperlink-source to build the documentation, using the haddock that is shipped with ghc (2.9.2 at the moment). Greetings, Joachim -- Joachim "nomeata" Breitner Debian Developer nomeata(a)debian.org | ICQ# 74513189 | GPG-Keyid: 4743206C JID: nomeata(a)joachim-breitner.de | http://people.debian.org/~nomeata

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Re: [Haskell-cafe] Project Euler: request for comments
by KC 28 Aug '11

28 Aug '11

Think of the simplest version of the problem that isn't totally trivial. e.g. A one dimensional list of numbers. What would you do? Note: you only want to touch each element once. The 2 dimensional case could be handled by putting into lists: rows, columns, major diagonals, and minor diagonals. This isn't the fastest way of doing the problem but it has the advantage of avoiding "indexitis". On Fri, Aug 26, 2011 at 6:15 PM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: > Like: > 20*19*21*18 > is bigger than > 100*100*3*2 > ? > > If so I need to think about how to formalize it. > > Thanks for the hint. > > On Fri, Aug 26, 2011 at 8:55 PM, KC <kc1956(a)gmail.com> wrote: >> 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 >> > -- -- Regards, KC

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Modules and a main function
by michael rice 27 Aug '11

27 Aug '11

W/r/t the code below, would somebody please explain the sense of having a main function in a module that is not named Main.hs? Michael From: http://www.haskell.org/haskellwiki/State_Monad ============ module StateGame where import Control.Monad.State -- Example use of State monad -- Passes a string of dictionary {a,b,c} -- Game is to produce a number from the string. -- By default the game is off, a C toggles the -- game on and off. A 'a' gives +1 and a b gives -1. -- E.g -- 'ab' = 0 -- 'ca' = 1 -- 'cabca' = 0 -- State = game is on or off & current score -- = (Bool, Int) type GameValue = Int type GameState = (Bool, Int) playGame :: String -> State GameState GameValue playGame [] = do (_, score) <- get return score playGame (x:xs) = do (on, score) <- get case x of 'a' | on -> put (on, score + 1) 'b' | on -> put (on, score - 1) 'c' -> put (not on, score) _ -> put (on, score) playGame xs startState = (False, 0) main = print $ evalState (playGame "abcaaacbbcabbab") startState

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HJavaScript: representing build-in global function.
by Станислав Черничкин 27 Aug '11

27 Aug '11

Hi Cafe! Does someone know how to represent js build-in global function (such as parseInt(), parseFloat(), eval()) with HJavaScript? Perhaps JConst: JCall (JConst "parseInt") (JString "123")? -- Sincerely, Stanislav Chernichkin.

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Project Euler: request for comments
by Oscar Picasso 27 Aug '11

27 Aug '11

Hi, I order to improve my Haskell skills I started (again) to solve the project euler problems with this language. I am now at problem 11 and would really appreciate any comment about my code in order to make it more elegant or efficient. My solutions can be found here: http://fp.opicasso.com/tag/projecteuler Oscar Picasso

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Re: [Haskell-cafe] How to make callCC more dynamic
by oleg＠okmij.org 27 Aug '11

27 Aug '11

bob zhang wrote: > I thought the right type for ContT should be > newtype ContT m a = ContT {runContT :: forall r. (a-> m r) -> m r} > and > other control operators > shift :: Monad m => (forall r . (a-> ContT m r) -> ContT m r) -> ContT m a > reset :: Monad m => ContT m a -> ContT m a > callCC :: ((a-> (forall r . ContT m r)) -> ContT m a) -> ContT m a > unfortunately, I can not make callCC type check, and don't know how to > do it. Precisely that problem was discussed in http://okmij.org/ftp/continuations/undelimited.html#proper-contM Your ContT is CPS1 in the above article. The article shows why you cannot write callCC with the above type of ContT. The article talks about other types. BTW, if you faithfully defined the monad for undelimited control than shift/reset cannot be expressed. Undelimited continuations are strictly less expressible than delimited ones. The above page gives the pointers to the papers with the proof.

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Re: [Haskell-cafe] Project Euler: request for comments
by KC 27 Aug '11

27 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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