Haskell-Cafe

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haskell-cafe@haskell.org

May 2006

114 participants
92 discussions

database access recommendation
by Brock Peabody 02 May '06

02 May '06

I'm teaching myself Haskell, and was wondering if anyone could recommend a library for accessing databases, PostgreSQL in particular. I looked at http://www.haskell.org/haskellwiki/Libraries_and_tools, and HSQL looked promising, but I can't get it to install on Windows or FreeBSD, with Hugs or GHC. According to the FreeBSD ports system, it is marked as broken. It fails with Hugs on both platforms on the "runhugs Setup.lhs configure" step in the base HSQL library with: FreeBSD: ERROR "/usr/local/lib/hugs/libraries/Text/ParserCombinators/ReadP.hs":133 - Syntax error in type expression (unexpected `.') Windows: ERROR "C:\Program Files\WinHugs\libraries\Text\ParserCombinators\ReadP.hs":156 - Syntax error in type expression (unexpected `.') GHC crashes with no error on the "runghc Setup.lhs build" step in the base HSQL library in Windows. In FreeBSD I can completely build and install the base library, but in any of the database specific directories, "runghc Setup.lhs configure" yields: "Setup.lhs:17:71: Couldn't match `PackageDescription' against `LocalBuildInfo' Expected type: Args -> ConfigFlags -> LocalBuildInfo -> IO ExitCode Inferred type: [String] -> ConfigFlags -> PackageDescription -> LocalBuildInfo -> IO ExitCode In the `postConf' field of a record In the record update: defaultUserHooks {preConf = preConf, postConf = postConf} <interactive>:1:87: Failed to load interface for `Main': Bad interface file: Setup.hi Setup.hi: openBinaryFile: does not exist (No such file or directory)" Thanks, Brock

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Newbie: Haskell Sine Oddities
by Aditya Siram 01 May '06

01 May '06

The Sine function in the prelude is not behaving as I expected. In the following Hugs session I tested sin on 0, 90,180 & 360 degrees. Prelude> sin 0 0.0 --correct Prelude> sin (pi/2) 1.0 --correct Prelude> sin pi 1.22460635382238e-16 --WRONG! Prelude> sin (2*pi) -2.44921270764475e-16 --WRONG! Is this normal behaviour? Or am I using the trig functions in an unexpected way? Thanks... Deech

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