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Re: matrix computations based on the GSL
by Keean Schupke 09 Jul '05

09 Jul '05

Is a matrix is a linear operation on a vector, does it not make sense to define matrix applicaion: mapply :: Matrix -> Vector -> Vector Then you can define say: rotate90 = mapply rotationMatrix90 v' = rotate90 v Keean.

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RE: [Haskell-cafe] Overlapping Instances with Functional Dependencies
by Simon Peyton-Jones 08 Jul '05

08 Jul '05

Martin's dead right. GHC uses a less sophisticated mechanism to do matching when it's thinking about functional dependencies than when it's doing straight instance matching. Maybe something cleverer for fundeps would make sense, as you point out. I hadn't thought of that before; it's a good point. Nowadays, whenever a fundep question comes up I think "how would it show up if we had associated type synonyms instead of fundeps?" (see the paper on my home page). In this case I think the answer is "GHC's current instance-matching mechanism would work unchanged"; or to put it another way, what ever mechanism is used for instance matching, the same would be used for type dependencies. Simon | I wouldn't call this a bug, overlapping instances | and in particular the combination with functional dependencies | are something which is not well studied yet. | Hence, GHC is very conservative here. | | I feel like you, this program should work. | As you correctly point out, there's a conflict among the | two improvement rules (resulting from the instances and FD). | A sensible decision is to apply the same "ad-hoc" | mechanism to improvement rules that is currently | applied to overlapping instances. Of course, we need some | formal system to express such conditions precisely. | You find some hints how to achieve this in | | G. J. Duck, S. Peyton-Jones, P. J. Stuckey, and M. Sulzmann. | Sound and decidable type inference for functional dependencies. | In Proc. of ESOP'04 | | Martin | | | Daniel Brown writes: | > I have the following three programs: | > | > class Foo a b | > instance Foo (a -> b) (a -> [b]) | > instance Foo a a | > | > class Bar a b | a -> b | > instance Bar (a -> b) (a -> b) | > instance Bar a a | > | > class Baz a b | a -> b | > instance Baz (a -> b) (a -> [b]) | > instance Baz a a | > | > When compiled in ghc 6.4 (with -fglasgow-exts | > -fallow-overlapping-instances -fallow-undecidable-instances) Foo | > and Bar compile fine, but Baz fails with this error: | > | > Baz.hs:2:0: | > Functional dependencies conflict between instance declarations: | > Baz.hs:2:0: instance Baz (a -> b) (a -> [b]) | > Baz.hs:3:0: instance Baz a a | > | > This is how I interpret the error: The fundep says "a uniquely | > determines b", but if you have `Baz (Int -> Int) b`, b is `Int -> [Int]` | > according to the first instance and `Int -> Int` according to the second | > instance. b isn't uniquely determined by a, so the functional dependency | > isn't functional -- thus the conflict. | > | > When confronted with overlapping instances, the compiler chooses the | > most specific one (if it is unique), e.g. `Baz (a -> b) (a -> [b])` is | > more specific than `Baz a a`. | > | > But it seems that the combination of the two features is broken: if the | > most specific instance is chosen before checking the functional | > dependency, then the fundep is satisfied; if the fundep is checked | > before choosing the most specific instance, then it isn't. | > | > Is this a bug, or am I confused? | > | > Dan | > _______________________________________________ | > Haskell-Cafe mailing list | > Haskell-Cafe(a)haskell.org | > http://www.haskell.org/mailman/listinfo/haskell-cafe | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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RE: [Haskell-cafe] Re: [Haskell] ANNOUNCE: GHC survey results
by Simon Peyton-Jones 06 Jul '05

06 Jul '05

| If anything I would like to see the Haskell community produce a Haskell | front end which was compiler neutral. That would facilitate many | interesting projects, and that might even help with the need to support | new extensions as they come along. There are already some candidates | floating around, but it seems they are not widely adopted. Well, "ghc -c -fext-core Foo.hs" is a Haskell front end that produces System F code ("External Core"), in a file Foo.hcr. I'm not sure whether that was what you meant. However, External Core doesn't seem to have really caught on. Only 5% said it was essential, with another 16% saying "nice to have". I'm sure there's room to improve the ExtCore route. Simon

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polymorphic type
by wenduan 06 Jul '05

06 Jul '05

Dear all, Suppose we have defined two functions as below: case :: (a -> c,b -> c) -> Either a b -> c case (f, g) (Left x) = f x case (f, g) (Right x) = g x plus :: (a -> b, c -> d) -> Either a b -> Either c d plus (f, g) = case(Left.f, Right.g) My question is regarding to the function signature of 'plus' , in its signature, does the 'a' in 'a -> b' and in 'Either a b', must be instantiated to the same object when the function is applied?E.g.,Either a b is instantiated to 'Either Char b', will the 'a' in 'a -> b' be instantiated to 'Either Char b'?Furthermore, are the two bs in 'a -> b' and 'Either a b' not conflicting?What I thought at first the signature of plus should be: plus :: (a -> c, b -> d) -> Either a b -> Either c d?Anyone know where I was wrong? -- X.W.D

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Cabal with Alex and and Happy
by Brian Smith 06 Jul '05

06 Jul '05

Is there an example of how to build a Cabal package that has a lexer generated with Alex and a parser generated with Happy? As far as I can tell, the way to do this is to add "Other-Modules: Module.Name.Of.Parser.y Module.Name.Of.Lexer.x" to each executable/library stanza. But, when I try this, I get: Could not find module `GHC.Exts': it is a member of package base-1.0, which is hidden The generated parser code contains: #if __GLASGOW_HASKELL__ >= 503 import GHC.Exts #else import GlaExts #endif Also, I don't see any way of passing options to preprocessors using Cabal. In particular, how do you pass options to Happy? I am using GHC and Cabal from the CVS head, built about two weeks ago. Thanks, Brian

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can't build module with ffi 'wrapper' by cabal (or ghc): unknown symbol
by Evgeny Chukreev 06 Jul '05

06 Jul '05

Hello! http://toril.ru/hmhash/hmhash-0.1.tar.bz2 ###### ./Setup.hs clean; ./Setup.hs configure; ./Setup.hs build -v5 Configuring HMhash-0.1... configure: searching for ghc in path. configure: found ghc at /usr/bin/ghc configure: looking for package tool: ghc-pkg near compiler in /usr/bin/ghc configure: found package tool in /usr/bin/ghc-pkg configure: Using install prefix: /usr/local configure: Using compiler: /usr/bin/ghc configure: Compiler flavor: GHC configure: Compiler version: 6.4 configure: Using package tool: /usr/bin/ghc-pkg configure: Using haddock: /usr/bin/haddock configure: Using happy: /usr/bin/happy configure: Using alex: /usr/bin/alex configure: Using hsc2hs: /usr/bin/hsc2hs configure: Using cpphs: /usr/bin/cpphs configure: Reading installed packages... configure: Dependency base-any: using base-1.0 Preprocessing library HMhash-0.1... /usr/bin/hsc2hs -osrc/Codec/Mhash.hs src/Codec/Mhash.hsc Building HMhash-0.1... /usr/bin/ghc -package-name HMhash -odir dist/build/src -hidir dist/build/src --make -isrc -ffi -fglasgow-exts -fallow-undecidable-instances -fallow-overlapping-instances -fallow-incoherent-instances -Wall -O0 -package base-1.0 Codec.Mhash -v Glasgow Haskell Compiler, Version 6.4, for Haskell 98, compiled by GHC version 6.2.2 Using package config file: /usr/lib/ghc-6.4/package.conf Using package config file: /home/akshaal/.ghc/i386-linux-6.4/package.conf Hsc static flags: -static *** Chasing dependencies: Chasing modules from: Codec.Mhash Stable modules: *** Compiling Codec.Mhash ( src/Codec/Mhash.hs, interpreted ): compile: input file src/Codec/Mhash.hs *** Checking old interface for Codec.Mhash: Compiling Codec.Mhash ( src/Codec/Mhash.hs, dist/build/src/Codec/Mhash.o ) *** Parser: *** Renamer/typechecker: <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' <no location info>: Warning: Defined but not used: `k' *** Desugar: Result size = 6135 *** Simplify: Result size = 6847 Result size = 5654 Result size = 5564 *** Tidy Core: Result size = 5564 *** CorePrep: Result size = 6911 *** Stg2Stg: *** CodeGen: *** CodeOutput: *** C Compiler gcc src/Codec/Mhash_stub.c -o /tmp/ghc29101.s -DDONT_WANT_WIN32_DLL_SUPPORT -v -S -Wimplicit -O -D__GLASGOW_HASKELL__=604 -ffloat-store -I src/Codec -I /usr/lib/ghc-6.4/include Reading specs from /usr/lib/gcc-lib/i486-linux/3.3.5/specs Configured with: ../src/configure -v --enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-gxx-include-dir=/usr/include/c++/3.3 --enable-shared --with-system-zlib --enable-nls --without-included-gettext --enable-__cxa_atexit --enable-clocale=gnu --enable-debug --enable-java-gc=boehm --enable-java-awt=xlib --enable-objc-gc i486-linux Thread model: posix gcc version 3.3.5 (Debian 1:3.3.5-8) /usr/lib/gcc-lib/i486-linux/3.3.5/cc1 -quiet -v -I src/Codec -I /usr/lib/ghc-6.4/include -D__GNUC__=3 -D__GNUC_MINOR__=3 -D__GNUC_PATCHLEVEL__=5 -DDONT_WANT_WIN32_DLL_SUPPORT -D__GLASGOW_HASKELL__=604 src/Codec/Mhash_stub.c -quiet -dumpbase Mhash_stub.c -auxbase-strip /tmp/ghc29101.s -O -Wimplicit -version -ffloat-store -o /tmp/ghc29101.s GNU C version 3.3.5 (Debian 1:3.3.5-8) (i486-linux) compiled by GNU C version 3.3.5 (Debian 1:3.3.5-8). GGC heuristics: --param ggc-min-expand=81 --param ggc-min-heapsize=95593 ignoring nonexistent directory "/usr/i486-linux/include" #include "..." search starts here: #include <...> search starts here: src/Codec /usr/lib/ghc-6.4/include /usr/local/include /usr/lib/gcc-lib/i486-linux/3.3.5/include /usr/include End of search list. *** Assembler gcc -Isrc/Codec -c /tmp/ghc29101.s -o dist/build/src/Mhash_stub.o *** Assembler gcc -Isrc/Codec -c /tmp/ghc29100.s -o dist/build/src/Codec/Mhash.o *** Deleting temp files Deleting: /tmp/ghc29101.s /tmp/ghc29100.s Upsweep completely successful. *** Deleting temp files Deleting: link(batch): upsweep (partially) failed OR Main.main not exported; not linking. *** Deleting temp files Deleting: /usr/bin/ar qv dist/build/libHSHMhash-0.1.a dist/build/src/Codec/Mhash.o /usr/bin/ar: creating dist/build/libHSHMhash-0.1.a a - dist/build/src/Codec/Mhash.o ###### ./Setup.hs install Installing: /usr/local/lib/HMhash-0.1 & /usr/local/bin HMhash-0.1... Registering HMhash-0.1... Reading package info from ".installed-pkg-config" done. building GHCi library /usr/local/lib/HMhash-0.1/HSHMhash-0.1.o... done. Saving old package config file... done. Writing new package config file... done. ###### ghci -package HMhash ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.4, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base-1.0 ... linking ... done. Loading package HMhash-0.1 ... linking ... ghc-6.4: /usr/local/lib/HMhash-0.1/HSHMhash-0.1.o: unknown symbol `CodecziMhash_d7Ew' ghc-6.4: unable to load package `HMhash-0.1' ------------------ I know how to fix it by hands: rm dist/build/libHSHMhash-0.1.a /usr/bin/ar qv dist/build/libHSHMhash-0.1.a dist/build/src/Codec/Mhash.o dist/build/src/Mhash_stub.o But, how to do it with cabal? -- ... WBR, Evgeny Chukreev ...

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Fork & execve
by yin 06 Jul '05

06 Jul '05

Hello! Is there some way how to fork a process in haskell? And excuting an another proces, waiting until it exit and colecting his stdout? Matej 'Yin' Gagyi PS: I'm sorry for my English!

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New-bee question about seq in Parsec.Pos
by Christoph Bauer 04 Jul '05

04 Jul '05

Hi, I try to understand, how Parsec works. In Pos.hs I found these definition of SourcePos: data SourcePos = SourcePos SourceName !Line !Column deriving (Eq,Ord) My poor haskell knowledge says me, that Line and Column is always strict. So, what does the following function? forcePos :: SourcePos -> SourcePos forcePos pos@(SourcePos name line column) = seq line (seq column (pos)) thanks for an enlightenment, Christoph Bauer -- let () = let rec f a w i j = Printf.printf "%.20f\r" a; let a1 = a *. i /. j in if w then f a1 false (i +. 2.0) j else f a1 true i (j +. 2.0) in f 2.0 false 2.0 1.0

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haskell parser for java bytecode?
by Kimberley Burchett 04 Jul '05

04 Jul '05

I'm interested in using haskell to do static analysis of java bytecode. To my surprise, I wasn't able to find any existing haskell libraries for parsing java .class files. Is anyone aware of such a library? I've already started writing my own implementation, which I intend to make available as a reusable library once it's ready, but if someone else has already done the work then I'd love to avoid having to repeat it. Kimberley Burchett http://www.kimbly.com/

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pair (f,g) x = (f x, g x)?
by wenduan 03 Jul '05

03 Jul '05

I came across a haskell function on a book defined as following: pair :: (a -> b,a -> c) -> a -> (b,c) pair (f,g) x = (f x,g x) I thought x would only math a single argument like 'a', 1, etc....,but it turned out that it would match something else, for example, a pair as below: square x = x*x pair (square.fst,Char.toUpper.snd) (2,'a') (4,'A') The type declaration of pair is what confused me, pair :: (a -> b,a -> c) -> a -> (b,c),it says this function will take a pair of functions which have types of a->b,a->c,which I would take as these two functions must have argument of the same type, which is a,and I didn't think it would work on pairs as in the above instance,but surprisingly it did,can anybody enlighten me? -- X.W.D

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