June 2012 - Haskell-Cafe

Install a script with Cabal?
by Ketil Malde 05 Jun '12

05 Jun '12

Hi, I have a small project that installs a couple of Haskell tools and a script that uses these. Cabal will of course build and install the Haskell programs, but how can I get Cabal to install the script as well? There's a host of UserHooks available¹, but it'd probably be better to have an example than to try to experiment with the right configuration. -k ¹ http://www.haskell.org/cabal/release/cabal-latest/doc/API/Cabal/Distributio… -- If I haven't seen further, it is by standing in the footprints of giants

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Installation of the New Haskell Platform
by Victor Miller 05 Jun '12

05 Jun '12

Before I install it (on on Mac OS X Lion) is there anything, manually, that I need to do in order to keep all of the cabal packages that I've installed, or are the reinstalled automatically? Victor

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ANNOUNCE: hquantlib-0.0.2.3
by Pavel Ryzhov 05 Jun '12

05 Jun '12

Hi Cafe, I'm pleased to announce that HQuantLib has been released recently after a year of sleep. This is mainly a technical release to clean up dependencies and refresh build infrastructure. The library is intended to be a functional port of QuantLib (http://quantlib.org) a free/open-source library for quantitative finance. Also I'd like to thank Nicholas Pezolano for contributing copulas to the library. Business changes highlights: ------------------------------ 1. Copulas in math methods. (CDS and CDO are expected in the next release) 2. Priceable interface for Instruments. (Option pricing to be done in further releases) ============================== Technical changes highlights: ------------------------------ 1. Version upgrade to recent GHC 7.4.1. 2. Dependency clean-ups. 3. Unit-test infrastructure. (HUnit + QuickCheck 2) ============================== SCM: https://github.com/paulrzcz/hquantlib Hackage: http://hackage.haskell.org/package/hquantlib Best regards, Pavel Ryzhov http://paulrz.cz

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Arithmetic expressions with GADTs: parsing
by j.romildo＠gmail.com 05 Jun '12

05 Jun '12

Hello. In order to learn GADTs, I have written the attached program, which defines a type for arithmetic expressions using GADTs, a parser for them, and an evaluation function. But my parser does not typecheck. ghc-7.4.1 gives me the error message: Expr.hs:25:28: Couldn't match expected type `Double' with actual type `Bool' Expected type: Bool -> Expr Double Actual type: Bool -> Expr Bool In the first argument of `(<$>)', namely `B' In the first argument of `(<|>)', namely `B <$> pBool' Any clues on how to fix that? Romildo

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Building gtk on OS/X with platform 2012.2.0.0
by Stuart Hungerford 05 Jun '12

05 Jun '12

Hi, Has anyone successfully cabal installed gtk (from gtk2hs) on OS/X Lion with platform 2012.2.0.0? I setup a new Lion instance with latest XCode and command line tools and Homebrew. I installed gtk+, Cairo, pango etc successfully with Homebrew. The following install log for gtk2hs-buildtools and gtk shows a compilation error (line 5431): http://hpaste.org/69521 I'm probably doing something wrong, so any advice much appreciated. Stu

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Re: [Haskell-cafe] Importing modules in GHCi
by Artyom Kazak 04 Jun '12

04 Jun '12

Oh, I’m sorry. I have Haskell Platform 2011.2.0.1, not 2012.2.0.1. So I guess it was a bug in GHCi…

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Haddock problems with Haskell-Platform2012.2.0.0
by cutsea110 04 Jun '12

04 Jun '12

Hi all. I installed ghc-7.4.1 and haskell-platform-2.12.2.0.0 on debian linux. I'm getting lots of complaints from 'ghc-pkg check', of the following form: ---- Warning: haddock-interfaces: /usr/pkg/share/doc/haskell- platform-2012.2.0.0/html/haskell-platform.haddock doesn't exist or isn't a file Warning: haddock-html: /usr/pkg/share/doc/haskell-platform-2012.2.0.0/ html doesn't exist or isn't a directory Warning: haddock-interfaces: /usr/pkg/share/doc/zlib-0.5.3.3/html/ zlib.haddock doesn't exist or isn't a file Warning: haddock-html: /usr/pkg/share/doc/zlib-0.5.3.3/html doesn't exist or isn't a directory ... ---- Any advice?

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Importing modules in GHCi
by Artyom Kazak 04 Jun '12

04 Jun '12

Hi Café, I would greatly appreciate your help. Entering the following in GHCi produces an error message… --> import Data.Time --> getCurrentTime >>= print <interactive>:1:20: No instance for (Show UTCTime) arising from a use of `print' Possible fix: add an instance declaration for (Show UTCTime) In the second argument of `(>>=)', namely `print' In the expression: getCurrentTime >>= print In an equation for `it': it = getCurrentTime >>= print …but when I create a file with `import Data.Time` in it, and load the file in GHCi, everything works as expected. Is it a bug in GHCi, or a feature? I’m using Haskell Platform 2012.2.0.1.

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Restricted Monad question
by Ismael Figueroa Palet 04 Jun '12

04 Jun '12

Hi, I was wondering about defining a restricted monad, and found out this blog post: http://blog.omega-prime.co.uk/?p=127 In GHC 7.4.1 still the recommended way is using the rmonad package, right? I guess the tricks with ConstraintKinds explained in the blog are used for internal implementation of RMonad? Thanks -- Ismael

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Edmonton Functional Programming Users Group meets June 5
by Kevin Charter 04 Jun '12

04 Jun '12

Hi Cafe, The Edmonton Functional Programming Users Group (EFPUG) is meeting tomorrow, June 5, at 6:00pm in room CS 2-49 of the Computing Science building on the University of Alberta north campus. We'll be having a hack night, exploring combinator parsing with a variety of combinator libraries, including Parsec, attoparsec, uu-parsinglib, and parsatron, a Clojure library inspired by Parsec. Everyone is welcome. https://groups.google.com/forum/?fromgroups&hl=en#!forum/edmonton-functiona… Kevin -- Kevin Charter kevin.charter(a)acm.org

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