October 2009 - Libraries

ghci can't find Paths_ module created by cabal
by Robin Green 26 Oct '09

26 Oct '09

I'm trying to run cabal-install in ghci so I can run it under the ghci debugger. However I try it, though, I always get one of these two errors: /src/greenrd/darcs/cabal-install/Main.hs:70:17: Could not find module `Paths_cabal_install': Use -v to see a list of the files searched for. Failed, modules loaded: none. or <command line>: Could not find module `Main': Use -v to see a list of the files searched for. -- Robin

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Rewrite of Data.Char library?
by Ahn, Ki Yung 26 Oct '09

26 Oct '09

In the #haskell IRC channel, we just had a discussion on Data.Char predicates such as isAlpha, isUpper, isLower. The implementation of Data.Char is not Haskell 98 since Char specification in Haskell 98 only covers latin1. However, current predicates are confusing and intuitive properties does not hold. One example is this: [17:53:32] <newsham> > let cs = [minBound..maxBound]; us = filter isUpper cs; ls = filter isLower cs in take 5 $ (map toUpper ls) \\ us [17:53:33] <lambdabot> "\170\186\223I\312" isLower '\170' == True but you can't turn that into an uppercase letter. isUpper '170' == '\170'. I know that GHC team working on a rewrite of IO library for better Unicode support (I hope also includes better locale and charset support). Along the line to the new IO library work, it would also be good to have some cleanup in the Data.Char as well. Thanks, Ahn, Ki Yung

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Re: cvs.haskell.org misconfigured
by Ian Lynagh 26 Oct '09

26 Oct '09

On Sun, Oct 25, 2009 at 07:52:52AM -0700, Paul Heinlein wrote: > > Anyway, anonymous cvs is working again. Great, thanks Paul! Thanks Ian

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cvs.haskell.org misconfigured
by Svein Ove Aas 25 Oct '09

25 Oct '09

The pserver at cvs.haskell.org appears to be misconfigured, in that anonymous login as described on the main cvs.haskell.org page is impossible. As I'm apparently the new maintainer for haskell-mode, I need access there of some kind or another in order to migrate haskell-mode to darcs; read-only is fine, though. Sincerely, -- Svein Ove Aas

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debugtracehelpers Re: traceM and traceShowM
by Thomas Hartman 20 Oct '09

20 Oct '09

I have this and a couple other handy functions in DebugTraceHelpers: http://patch-tag.com/r/tphyahoo/DebugTraceHelpers/snapshot/current/content/… hackage: http://hackage.haskell.org/packages/archive/DebugTraceHelpers/0.12/doc/html… 2009/10/16 Martijn van Steenbergen <martijn(a)van.steenbergen.nl>: > Hello, > > I propose the addition of the following two functions to module Debug.Trace: > >> traceM :: Monad m => String -> m () >> traceM msg = trace msg (return ()) >> >> traceShowM :: (Show a, Monad m) => a -> m () >> traceShowM = traceM . show > > These functions allow tracing in any do-block. I often define them myself; I > think they are useful in general. > > Deadline: 23 October 2009. > > Martijn. > _______________________________________________ > Libraries mailing list > Libraries(a)haskell.org > http://www.haskell.org/mailman/listinfo/libraries >

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Would you review/test my FFI library?
by Maurício CA 17 Oct '09

17 Oct '09

Hi, I've been working over the last months in what I call a "preprocessor DSL for Haskell FFI" :) It started as a crude attempt, with many problems. But by now it has evolved and been sharped into something that I want to recomend as a professional quality tool for practical FFI. By professional, I just mean it generates reliable, predictable code, and the code you write using it is portable and extremely easy to write and, even more, maintain. I have to warn: it isn't really intelectually exciting. Don't waste your time with it, unless you have a recurrent need for FFI. I started it from a professional need, and it's not more than a small set of preprocessor macros for hsc2hs. I have been able to use it, though, to get bindings to very extensive C libraries in just a few hours. The main idea in this tool is to shift the way Haskell power is applied over C code. Instead of mixing Haskell code and C names, we write an almost transparent layer over C. On top of that, we will then write our Haskell code. Although that FFI layer is just "C on Haskell", you get a lot of flexibility in the Haskell cover. Here it is, documentation, hackage package and an example from DirectFB types: http://bitbucket.org/mauricio/bindings-common http://hackage.haskell.org/package/bindings-common http://bitbucket.org/mauricio/bindings-directfb/src/tip/src/Bindings/Direct… I appreciate any comments you have, specially problems you see. Thanks, Maurício

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Can it write an interpreter without building the tree of parse?
by Daneel Yaitskov 17 Oct '09

17 Oct '09

Hi, I learn Parsec library now. Parsers from all articles which I found at first parse input stream entirely and only then call an eval function. Such method requires to define many data-types for each an element of a language. And I guess that it hard to write bash interpreter with it help. Bash makes immediately its commands. For example: #!/bin/bash echo HEELLO ) echo DDDD dan@tmp$ bash a.sh HEELLO a.sh: line 5: syntax error near unexpected token `)' a.sh: line 5: `)' dan@tmp$ First command of the script is made by bash nonetheless the error in the next line. I want to write a interpreter which does actions (IO) inside the parse function. But I don't know how to do it. That code show that What I need. Does trick exist that the block function can contain an action (putStr)? import Text.ParserCombinators.Parsec import Data.Map interpret s = runParser mainf () "" s mainf :: GenParser Char () (IO ()) mainf = do rr <- block eof return $ putStrLn rr block :: GenParser Char () String block = do s <- string "HELLO WORLD" ----- putStrLn "There is an action" return s Daneel Yaitskov.

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Re: traceM and traceShowM
by Martijn van Steenbergen 16 Oct '09

16 Oct '09

pepe wrote: > But traceM will only work on non-lazy monads, such as Either or Maybe. That's exactly what you expect from a call to trace: if it doesn't get evaluated, its message isn't output. Martijn.

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Add instance IsString ShowS where fromString = showString
by Bas van Dijk 14 Oct '09

14 Oct '09

Hello, It would be really nice to use OverloadedStrings when constructing a ShowS, for example in a definition of showsPrec in an instance for Show. The patch attached in the ticket[3544] adds the necessary instance to base/GHC/Show.lhs: instance IsString ShowS where fromString = showString Note that this does require TypeSynonymInstances. Discussion period 2 weeks. regards, Bas [3544] http://hackage.haskell.org/trac/ghc/ticket/3544

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Haskell Platform web page could be more informative
by David Menendez 08 Oct '09

08 Oct '09

Since the Haskell Platform is (or will become) the recommended way to install Haskell for inexperienced users, I am concerned about how difficult it is to find information about the Platform from its primary web page at <http://hackage.haskell.org/platform/>. For example, it's not obvious how a non-expert user would find answers to these questions: 1. Where should I send questions about the Haskell Platform? The only contact information provided is the bug tracker. 2. When was the last release of the Haskell Platform? A new user, seeing the version number 2009.2.0.2, is more likely to think "February" than "August". 3. When is the next release of the Haskell Platform? 4. How often are releases scheduled? 5. What is new in the current release? 6. What will be included in the next release? If that isn't known yet, when will it be known? 7. Are there any outstanding issues I should know about? (For example, do I need to manually edit /usr/bin/ghc after installation on any particular platforms?) Note: I am not looking for answers to these questions (except maybe 3 and 5). My concern is that this information is not readily available. -- Dave Menendez <dave(a)zednenem.com> <http://www.eyrie.org/~zednenem/>

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