- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Tests by properties: origin?
by Janis Voigtländer 05 Jun '12

05 Jun '12

Am 01.06.2012 12:00, schrieb Yves: > Out of curiosity, does someone know if QuickCheck was the first test > framework working through test by properties associated with random > generation or if it drew the idea from something else? > > Because the idea has be retaken by a lot of frameworks in several languages > (seehttp://en.wikipedia.org/wiki/Quickcheck) but I can't find what was > QuickCheck inspiration. How about reading the original paper introducing QuickCheck? If the authors drew inspiration from elsewhere, the paper is for sure where they would tell you, first hand. :-) Best, Janis. -- Jun.-Prof. Dr. Janis Voigtländer http://www.iai.uni-bonn.de/~jv/

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attoparsec double precision, quickCheck and aeson
by Warren Harris 05 Jun '12

05 Jun '12

The double parser provided by Data.Attoparsec.ByteString.Char8 looses precision around the 13-15th decimal place (http://hackage.haskell.org/packages/archive/attoparsec/0.10.2.0/doc/html/Da…) Unfortunately this reeks havoc with my attempts to write a quickCheck test that validates print-read equivalence for a program that uses Aeson. I have tried compensating for this round-off error in my quickCheck generator using a function like this: roundDouble :: Double -> Double roundDouble d = let Right v = A8.parseOnly A8.double (C.pack (show d)) in v which helps in many cases, but for some the parsing seems bi-stable, alternating between two imprecise double values and causing the test to fail. I was wondering if anyone could suggest a better work-around for this problem, or explain why Attoparsec's double parser can't be isomorphic to haskell's. Thanks, Warren

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Extending constraints
by Bas van Dijk 05 Jun '12

05 Jun '12

Hello, I have the following program: -------------------------------------------------------------------------- {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE ScopedTypeVariables #-} import Data.Proxy (Proxy) import Data.Typeable (Typeable, TypeRep, typeOf) data ProxyWrapper constraint = forall a. constraint a => ProxyWrapper (Proxy a) typeOfInnerProxy :: ProxyWrapper constraint -> TypeRep typeOfInnerProxy (ProxyWrapper p) = typeOfArg p typeOfArg :: forall t a. Typeable a => t a -> TypeRep typeOfArg _ = typeOf (undefined :: a) -------------------------------------------------------------------------- Type checking this gives the following expected type error: ProxyWrapper.hs:12:37: Could not deduce (Typeable a) arising from a use of `typeOfArg' from the context (constraint a) bound by a pattern with constructor ProxyWrapper :: forall (constraint :: * -> Constraint) a. (constraint a) => Proxy a -> ProxyWrapper constraint, in an equation for `typeOfInnerProxy' Is there a way to extend the 'constraint' with the 'Typeable' constraint in the type signature of 'typeOfInnerProxy'? Regards, Bas

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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 05 Jun '12

05 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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