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ghc error: requested module name differs from name found in interface file
by Larry Evans 22 Oct '08

22 Oct '08

With a file containing: > module Main where > > import Array > import Control.Functor.Fix I get: > make > ghc -i/root/.cabal/lib/category-extras-0.53.5/ghc-6.8.2 -c catamorphism.example.hs > > catamorphism.example.hs:19:0: > Bad interface file: /root/.cabal/lib/category-extras-0.53.5/ghc-6.8.2/Control/Functor/Fix.hi > Something is amiss; requested module main:Control.Functor.Fix differs from name found in the interface file category-extras-0.53.5:Control.Functor.Fix > make: *** [all] Error 1 I used cabal to install category-extras: > /home/evansl/download/haskell/libs # cabal install category-extras > Resolving dependencies... > Downloading category-extras-0.53.5... > Configuring category-extras-0.53.5... > Preprocessing library category-extras-0.53.5... ... > /usr/bin/ar: creating dist/build/libHScategory-extras-0.53.5.a > Installing library in /root/.cabal/lib/category-extras-0.53.5/ghc-6.8.2 > Registering category-extras-0.53.5... > Reading package info from "dist/installed-pkg-config" ... done. > Saving old package config file... done. > Writing new package config file... done. > /home/evansl/download/haskell/libs # What should I do to import the Functor.Fix as shown here: http://comonad.com/reader/2008/recursion-schemes/ TIA. -Larry

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Verifying a list of properties using QuickCheck
by Thomas van Noort 22 Oct '08

22 Oct '08

Hi, I would like to verify a list of properties using QuickCheck. Of course, I can test a single property using: quickCheck :: Testable prop => prop -> IO () Then, I can check a list of properties my mapping this function over a list: quickCheckL :: Testable prop => [prop] -> IO () quickCheckL = mapM_ quickCheck This gives me a result for each property: Prelude Test.QuickCheck> quickCheckL [1==1,2==2] OK, passed 100 tests. OK, passed 100 tests. However, I would like a single result for the complete list of properties instead of a result for each property. I realize that this restricts the properties to be of the same type, but that isn't a problem for my application. Did I miss a library function that provides me this functionality? Regards, Thomas

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ANNOUNCE: rewriting-0.1
by Thomas van Noort 22 Oct '08

22 Oct '08

Generic rewriting library for regular datatypes =============================================== This package provides rewriting functionality for regular datatypes. Regular datatypes are recursive datatypes such as lists, binary trees, etc. This library cannot be used with mutually recursive datatypes or with nested datatypes. This library has been described in the paper: A Lightweight Approach to Datatype-Generic Rewriting. Thomas van Noort, Alexey Rodriguez, Stefan Holdermans, Johan Jeuring, Bastiaan Heeren. ACM SIGPLAN Workshop on Generic Programming 2008. More information about this library can be found at: http://www.cs.uu.nl/wiki/GenericProgramming/Rewriting Features -------- * Generic rewriting machinery * Generic traversals (top-down, bottom-up, etc.) * Rewrite rules are defined concisely as values instead of functions, which allows for better observability * Rewrite rules are defined in the original domain and do not require a manual extension for metavariables Requirements ------------ * GHC 6.10.1 (tested with 6.10.0.20081007) * Cabal 1.2.1 (or higher) Download & Source ----------------- Use cabal-install: cabal install rewriting Get the package: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/rewriting Get the source: svn checkout https://svn.cs.uu.nl:12443/repos/dgp-haskell/rewriting Bugs & Support -------------- Report issues, request features, or just discuss the library with the authors, maintainers, and other interested persons at: http://www.haskell.org/mailman/listinfo/generics

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Fwd: enhancing type classes with properties
by Alberto G. Corona 22 Oct '08

22 Oct '08

I´m just thinking aloud, but, because incorporating deeper mathematics concepts has proven to be the best solution for better and more flexible programming languages with fewer errors, I wonder if raising the type classes incorporating axioms can solve additional problems. At first sight it does: class Abelian a where (+) :: a -> a -> a property ((+))= a+b == b+a this permits: 1- safer polimorphism: I can safely reuse the operator + if the type and the property is obeyed. The lack of ability to redefine operators is a problem for DSLs that must use wreid symbols combinations with unknow meanings. To use common operators with fixed properties is very good. the same aplies for method names. 2- the compiler can use the axions as rewrite rules. 3- in debugging mode, it is possible to verify the axiom for each value a generated during execution. Thus, a generator is not needed like in quickcheck. The logic to quickcheck can be incorporated in the debugging executable. 3 guaranties that 1 and 2 are safe. a type class can express a relation between types, but it is not possible to define relation between relations.

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Build without install, using cabal
by Mauricio 22 Oct '08

22 Oct '08

Hi, I would like to include a few source files as 'executable' sections in a .cabal package description. However, although I do want to use main=mainDefault features, I do not want those packages to be installed when I run 'Setup.hs install'. Is it possible to do that? I believe there's no flag that indicates install step, since (I guess) flags are checked only at configure time. Thanks for your help, Maurício

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labels in HList
by roger peppe 22 Oct '08

22 Oct '08

hi, i'm trying to get labelled records working with the current version of HList. i've got code that looks like: >{-# language EmptyDataDecls #-} >module Tst where > import Data.HList > > data Foo; foo = proxy::Proxy Foo > data Bar; bar = proxy::Proxy Bar > rec1 = > foo .=. 1 .*. > bar .=. "hello" .*. > emptyRecord which gives me the error: Tst4.hs:8:2: No instance for (HEq (Proxy Foo) (Proxy Bar) HFalse) arising from a use of `.*.' at Tst4.hs:(8,2)-(10,12) Possible fix: add an instance declaration for (HEq (Proxy Foo) (Proxy Bar) HFalse) In the expression: foo .=. 1 .*. bar .=. "hello" .*. emptyRecord In the definition of `rec1': rec1 = foo .=. 1 .*. bar .=. "hello" .*. emptyRecord some discussion on #haskell suggesting importing Label4 and TypeEqGeneric1 but a) that's not possible because both are hidden inside the HList package and b) even when i get around that restriction, i still get a "No instance for (TypeCast HFalse HFalse)" error. thanks, rog.

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code generation
by z ghost 22 Oct '08

22 Oct '08

hello, im interested in using haskell to generate code and make little AI applications for fun.. is anyone already doing this sort of thing? it would be fun to collaborate with people on this. Here's some code as an example of the direction i'd like to go in. It builds up template haskell Exps and uses the Hint module to typecheck them. With some more work, it could be turned into a program that finds haskell programs (given a type as input).. http://www.sendspace.com/file/aj5r38 __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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cabal-install question
by Ken98 21 Oct '08

21 Oct '08

Hello, I recently started using cabal-install to install packages. However, ran into a problem today trying to install ftphs where the current HUnit dependency required base (==4). I'm using ghc-6.8.2 on ubuntu. To get around this, I looked through previous versions of HUnit and found that 1.2.0.0 was the last to have a successful build with ghc-6.8. So, I downloaded the tar.gz and did a runhaskell Setup.hs ... This worked and I was able to complete the ftphs install. So my question is, could I have used cabal install to specify the specific version of HUnit without having to do the manual download/configure/build/install? Thanks, Ken -- View this message in context: http://www.nabble.com/cabal-install-question-tp20098091p20098091.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Installing ghc + gtk2hs on linux
by Bulat Ziganshin 21 Oct '08

21 Oct '08

Hello haskell-cafe, i'm linux freshman what's the simplest way to install ghc + gtk2hs on Ubuntu x86 system? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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FFI and GHCi
by Emil Axelsson 21 Oct '08

21 Oct '08

Hi, I'm making my first attempt at using some C code in my Haskell program. I need it because I have a large amount of small constant tables, and GHC takes ages to compile the if I use ordinary lists (and the object file gets huge). If there's any way of achieving this without going to C, I'd be interested to know. My question is about how to compile a library that contains C code. At the end of this message is a simple example of an 'increase' function. To compile, I run ghc Increase.hs --make -o increase increase.c and everything works as expected. But then when I want to load the example in GHCi, I need to give the object file at the command line ghci Increase increase.o or I get "unknown symbol `increase'" when I try to run main. It feels a bit awkward to have to list the object files every time I want to run GHCi. Is there any way of avoiding that? There must be, because if I install the files as a Cabal library, I can fire up GHCi without mentioning any object files. But I don't want to go through cabal every time I want test some part of my code. Thanks for any help, / Emil ---------------- increase.h: int increase(int x); increase.c: #include "increase.h" int increase(int x) { return x+1; } Increase.hs: {-# INCLUDE "increase.h" #-} {-# LANGUAGE ForeignFunctionInterface #-} import Foreign.C foreign import ccall "increase.h increase" inc :: CInt -> CInt main = print (inc 2, inc 20) ----------------

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