August 2008 - Haskell-Cafe

How can I get the mutable array out of an IOUArray for FFI use?
by Ryan Ingram 02 Aug '08

02 Aug '08

I wrote some fast bit-twiddling functions in C because my Haskell performance wasn't good enough. Now I'm trying to recompile with GHC6.8.3 and failing. This code worked on GHC6.6.1. I get the following error: > ghc --make main.hs Bitmap.hs:11:7: Could not find module `Data.Array.IO.Internals': it is hidden (in package array-0.1.0.0) I suppose I can declare a copy of the internal type and use unsafeCoerce#, but that seems like a terrible idea if there is a better way. What's the right way to make this work? Can I force that module to be unhidden? Should I file a GHC bug? -- ryan {-# OPTIONS_GHC -fffi -fglasgow-exts #-} {-# INCLUDE "bitmap_operations.h" #-} module Bitmap ( clearBitmap, ) where import Foreign.Ptr import Data.Array.Base import Data.Array.IO.Internals import GHC.Exts import Data.Word foreign import ccall unsafe clear_bitmap :: MutableByteArray# RealWorld -> Word32 -> Word32 -> IO () {-# INLINE unsafeGetMutableArray# #-} unsafeGetMutableArray# :: IOUArray Int Word32 -> MutableByteArray# RealWorld unsafeGetMutableArray# (IOUArray (STUArray _ _ array#)) = array# clearBitmap :: IOUArray Int Word32 -> Word32 -> Word32 -> IO () clearBitmap a1 color size = clear_bitmap (unsafeGetMutableArray# a1) color size

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Using fundeps to resolve polymorphic types to concrete types
by Bryan Donlan 02 Aug '08

02 Aug '08

Hi, Is there any theoretical reason that functional dependencies can't be used to resolve a polymorphic type to a concrete type? For example: > -- compile with -fglasgow-exts > > class DeriveType a b | a -> b > > data A = A > data B = B > > instance DeriveType A B > > simpleNarrow :: DeriveType A b => b -> B > simpleNarrow = id Since 'b' is uniquely determined by the fundep in DeriveType, it seems that this ought to work; ie, since the only type equation satisfying DeriveType A b is B -> B, it should reduce to that before trying to fit its type against its body. The motivation is this case: > data ComplexType a where > SomeConstructor :: DeriveType a b => a -> b -> ComplexType a > > specialCaseFunc :: ComplexType A -> B > specialCaseFunc (SomeConstructor _ b) = b Essentially, if I have a data structure with two types used as fields, and one uniquely determines the other, I'd like to use these instances to avoid re-stating the implied one in the type equations, if possible. Is there some theoretical reason for this not to work, or is it just a limitation of GHC's current implementation? (Note, I'm testing with GHC 6.8.2, so it's possible this might be fixed in trunk already...) Thanks, Bryan Donlan

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question about "faulting in" Haskell packages ...
by Galchin, Vasili 02 Aug '08

02 Aug '08

Hello, Sorry I asked this question before .. say I want to install package A that depends on package B, C, D but maybe B and D are not installed on my machine. Basically I want to "fault in" (i.e. install automatically) in B and D with "no fuss no muss". ??? In reality I would like to get my laptop which is running Ubuntu totally "faulted up" with all Haskell packages ... ;^) Regards, Vasili

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Cabal files on Windows
by John Lato 01 Aug '08

01 Aug '08

Hello, Can anyone point me to a method for including path names with spaces in a cabal file? I would like to add a line similar to the following: include-dirs: C:\Program Files\program\include and of course a corresponding library as well. I've tried various methods of escaping the space and quoting, and nothing seems to work. Is this possible at all? I'm using Cabal-1.2.4.0 on Windows. I've tried running with a Windows shell and MSYS bash, with the same results. Thanks, John Lato

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Analysing Haskell Program
by Roberto D'Aprile 01 Aug '08

01 Aug '08

Hello to everybody I'm using haskell for some research work and now i need to evaluate the performance of some simple haskell programs in particular information on the like, CPU cycles, bus usage, memory access and so on; so i wish to know if there is a way to compile haskell programms so they can be used with simplescalar or if there is another tool which i can use. Thank you

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category theory tutorial pdfs .....
by Galchin, Vasili 01 Aug '08

01 Aug '08

Hello, Prof. Harold Simmons' tutorial IMO are like a Russian matroshka doll ... first layer is for newbie ... inner layers require more sophistication. IMO a very subtle writer ... I have every book imaginable on cat theory and topos theory so I think can compare a little. 1) http://www.cs.man.ac.uk/~hsimmons/BOOKS/books.html ... an earlier version ... "An Intro to Category Theory in Four Easy Movements" ... this version delves a little into Topos Theory ... pretty subtle .. cool 2) http://www.cs.man.ac.uk/~hsimmons/MAGIC-CATS/magic-cats.html ... newer version which also has its cool merits IMO! Regards, Vasili

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a really dumb posting question ;^(
by Galchin, Vasili 01 Aug '08

01 Aug '08

Hello, What do I do to do a followup haskell cafe posting? E.g. I want to put a posting on the category theory thread! Kind regards, Vasili

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an array of pointers in FFI?
by Galchin, Vasili 01 Aug '08

01 Aug '08

Hello, Is a (Ptr (Ptr a)) a polymorphic representation of an array of pointers of type "a"? I want to pass an array of pointers to a C function. Kind regards, Vasili

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