- Haskell-Cafe - Haskell.org

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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An attempt at an EDSL for platform independent 3D animation
by C K Kashyap 04 Jun '12

04 Jun '12

Hi All, I've written a Haskell program that allows you to describe "dance movements" and it spits out javascript that does animation on an HTML 5 canvas (that's the platform independent bit). https://github.com/ckkashyap/Dancer Please do check it out and let me know what you think - all you'd need is Haskell platform. It's really preliminary at this point - The only animation that I've built using it is "walk" - this makes a matchstick man walk (you have to stretch your imagination a bit). Regards, Kashyap

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FP freelancers group on linkedin
by Ivan Perez 04 Jun '12

04 Jun '12

Hi, A while ago somebody posed the question "What if you get hit by a bus", regarding the apparent lack of Haskell developers that could continue somebody's work if something happened to them. I just created a linkedin group for FP programmers available for hire on a per-project basis ([1]). I hope this enables new collaborations among us, and also that it helps potential clients understand that there are many Haskell professionals available and that they need not fear this language. I also think this may complement the great listing at haskellers.com created by snoyberg, as well as other linkedin groups related to FP. I'd be happy to add links to other "directories" on the group's description page. I'm open to suggestions. Regards, Ivan. [1] http://www.linkedin.com/groups/Functional-programming-freelancers-consultan…

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