- Haskell-Cafe - Haskell.org

minimal interface
by Sean McLaughlin 03 Mar '10

03 Mar '10

Hello, I have a midsize program, and would like to simplify the module interfaces for my own sanity. I know there are tools to check for extraneous imports, but is there something similar for exports? For instance, if module A exports f, but A.f is never used in my compiled program, I would like to be warned of this fact. Thanks, Sean

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segmentation fault with ghc-6.10.4 on linux-x86_x64
by Wim Vanderbauwhede 03 Mar '10

03 Mar '10

Hello, I'm writing a compiler and it segfaults when compiled with ghc-6.10.4 on linux-x86_x64. It runs fine when compiled with ghc-6.10.4 on Mac OS X 10.5 (64-bit Intel) and with ghc-6.8.2 on Mac OS X 10.4 (32-bit PPC). I use the Haskell platform, the ghc -v output is Glasgow Haskell Compiler, Version 6.10.4, for Haskell 98, stage 2 booted by GHC version 6.8.2 Using package config file: /usr/local/lib/ghc-6.10.4/./package.conf Using package config file: /users/wim/.ghc/x86_64-linux-6.10.4/package.conf hiding package base-3.0.3.1 to avoid conflict with later version base-4.1.0.0 hiding package network-2.2.1.2 to avoid conflict with later version network-2.2.1.4 hiding package time-1.1.2.4 to avoid conflict with later version time-1.1.4 wired-in package ghc-prim mapped to ghc-prim-0.1.0.0 wired-in package integer mapped to integer-0.1.0.1 wired-in package base mapped to base-4.1.0.0 wired-in package rts mapped to rts-1.0 wired-in package haskell98 mapped to haskell98-1.0.1.0 wired-in package syb mapped to syb-0.1.0.1 wired-in package template-haskell mapped to template-haskell-2.3.0.1 wired-in package dph-seq mapped to dph-seq-0.3 wired-in package dph-par mapped to dph-par-0.3 The offending code is (simplified) mapM emit (sc_args sc) with sc::ServiceCall data ServiceCall = MkServiceCall { sc_args::[Expr], ... } data Expr = PureE (PString String) | ... and emit defined via a type class EmitG: emitExpr (PureE e) = emit e instance EmitG Expr where emit = emitExpr emitPureExpr (PString s) = return $ show s instance EmitG PureExpr where emit = emitPureExpr So it actually maps "show" over a list of strings. The compiler parses a test program, the segfault occurs when emitting code for lines like ImgBlock() img1 = img.in("img.raw"); (a "service call" in my language) Replacing the string by a number of any other type of the AST makes no difference. It looks like a bug in ghc's memory allocation. Any suggestions on how to debug this? Thanks! Wim

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how to send a string to a tuple
by Pradeep Wickramanayake 03 Mar '10

03 Mar '10

Hi I have taken a string output from a file But I want to send that string to another function which will convert in to a tuple Can someone teach me please

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Monad laws
by David Sabel 03 Mar '10

03 Mar '10

Hi, when checking the first monad law (left unit) for the IO-monad (and also for the ST monad): return a >>= f ≡ f a I figured out that there is the "distinguishing" context (seq [] True) which falsifies the law for a and f defined below > let a = True > let f = \x -> (undefined::IO Bool) > seq (return a >>= f) True True > seq (f a) True *** Exception: Prelude.undefined Is there a side-condition of the law I missed? Regards, David

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using haskell to serve with apache
by brad clawsie 03 Mar '10

03 Mar '10

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 hi i'm currently doing some work on a personal site and was considering giving a haskell web tool a spin. i have a fairly complex apache configuration, so i don't want to try to replace it with a native haskell server, but instead use haskell via an interface to apache (i.e. something like wsgi, plack, etc). some searching shows hyena and yesod in various states of development, but i can't figure out if they are appropriate or ready for use. anyone have experiences using haskell behind apache? should i just try out something based on fastcgi? any anecdotes welcome thanks brad -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (FreeBSD) iEYEARECAAYFAkuKoJEACgkQxRg3RkRK91PVJwCdFD4dS47KjJuMcNVZmPkYXKyU ItsAnRoYBE39XtXyXDluh+pHSxzP+Qcd =91Ql -----END PGP SIGNATURE-----

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references for compiler optimizations for functional languages
by Michael Vanier 03 Mar '10

03 Mar '10

Hi everyone, I'm interested in collecting good references for compiler optimizations for functional languages (lazy, strict, statically-typed or not). Any suggestions? Thanks in advance, Mike

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new syntax highlighting library (lexers wanted!)
by John MacFarlane 03 Mar '10

03 Mar '10

Cafe: I wanted to let you know about a new syntax highlighting library I've been working on, called 'illuminate'. The (BSD3 licensed) code is on github: http://github.com/jgm/illuminate illuminate is meant eventually to replace my other highlighting library, highlighting-kate, which is too big, slow, and memory-hungry. In my benchmarks, illuminate is around 70X faster than highlighting-kate and uses half the memory. It can produce output in ANSI, HTML, XHTML, and LaTeX. Highlighting styles can be defined independently of any output format. So far I've written lexers for haskell, literate haskell, cabal, alex, c, c++, c#, python, ruby, java, html, rhtml, xml, javascript, css, tex, and bibtex. Want to highlight a language not on this list? Why not help out by writing a lexer? (Study the lexer for a similar language to get started; if you aren't familiar with Alex, you may want to look at the Alex User Guide too. And let me know if you have any questions.) John

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FFI and lists?
by Kimberly Wallmark 03 Mar '10

03 Mar '10

I'm working with FFI to make a Haskell DLL that's called by C# code. I understand how to share simple types. I've found reasonable documentation for struct-equivalents. Is there a clean way to share lists, or should I make a linked-list struct and do it manually? In other words, if I have adder :: CInt -> CInt -> CInt adder x y = (x+y) then I can use foreign export stdcall adder :: CInt -> CInt -> CInt and on the other side it behaves like int adder(int a, int b); I'd like to know what to do if I have squares :: [CInt] -> [CInt] squares = map (^2) Advice? --Kim

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Evolving Faster Haskell Programs (now with LLVM!)
by Don Stewart 03 Mar '10

03 Mar '10

http://donsbot.wordpress.com/2010/03/01/evolving-faster-haskell-programs-no… … In which I use genetic algorithms to search for optimal LLVM optimizer passes to make Haskell programs faster … LLVM + GHC is a lot of fun. -- Don

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Fwd: [Haskell-cafe] minimal interface
by Sean McLaughlin 02 Mar '10

02 Mar '10

Hi Don, This doesn't tell me what is extraneous in the exports. For instance If I have two modules A and Main module A (f, g) where f :: a -> a f = id g :: a -> a g = id module Main (main) where import qualified A main :: IO () main = do let a = A.f 7 putStrLn $ show a I'd like something to tell me that A.g is not used in the program. Thanks, Sean On Tue, Mar 2, 2010 at 4:28 PM, Don Stewart <dons(a)galois.com> wrote: > seanmcl: > > Hello, > > > > I have a midsize program, and would like to simplify the module > interfaces > > for my own sanity. I know there are tools to check for extraneous > imports, but > > is there something similar for exports? For instance, if module A > exports f, > > but A.f is never used in my compiled program, I would like to be warned > of this > > fact. > > ghc -ddump-minimal-imports > > I think that's the flag. > > -- Dump >

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