- Glasgow-haskell-users

Problem compiling 6.8.1 extralibs
by Alexis Hazell 08 Nov '07

08 Nov '07

Hi all, i'm having some difficulties compiling the 6.8.1 extralibs on a Mandriva 2007.0 box. Despite happy 1.15 being installed (with the happy binary in /usr/bin/), i get the following error: Preprocessing library haskell-src-1.0.1.1... Setup: The program happy is required but it could not be found make[1]: *** [haskell-src/GNUmakefile] Error 1 make[1]: Leaving directory `/usr/src/ghc-6.8.1/libraries' make: *** [stage1] Error 2 Command exited with non-zero status 2 Any suggestions as to how to fix this would be greatly appreciated. :-) Alexis.

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Template Haskell documentation
by Richard Giraud 07 Nov '07

07 Nov '07

Hello I'm trying to learn how to use Template Haskell and I'm finding that the documentation is sparse. In particular, the constructors for Dec, Exp, Con, etc. in Language.Haskell.TH.Syntax aren't explained. Would documentation patches be welcomed for this library? Thanks, Richard

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Building a prelude
by Victor Nazarov 07 Nov '07

07 Nov '07

Is it possible to build Prelude from scratch. Or just some modules like GHC.Base. For example when I do % ghcjs-inplace.bat -fglasgow-exts -fjavascript -cpp -c Err.lhs-boot % ghcjs-inplace.bat -fglasgow-exts -fjavascript -cpp -c Base.lhs I've got this error: Base.lhs:94:0: Bad interface file: C:/Program Files/Visual Haskell\imports/GHC/Err.hi-boot Something is amiss; requested module base:GHC.Err differs from name found in the interface file main:GHC.Err What can I do to overcome this. Really what I want is to build some runtime system for my ghc-derived-javascript-compiler. And to embed JavaScript integers into it. I understand that I need to write some primitive operations in JavaScript like addition. I can build some numerals on the top of Haskell, but I'd like to get access to underlying javascript features and integers is a good point to start. Can you recommend me some strategy or smth? -- vir http://vir.comtv.ru/

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Why only inference in type checking?
by Philip K.F. Hölzenspies 07 Nov '07

07 Nov '07

Dear All, A while ago, I had trouble understanding the coverage condition and I raised a question on this mailing list. Help was swift and adequate, especially the reference to the paper entitled "Understanding Functional Dependencies via Constraint Handling Rules" was very useful. However, having considered the problem of non-termination of the type checker, I can't help but wonder why the type checker is "inference only." From the paper mentioned above, consider the following example: class Mul a b c | a b -> c where (*) :: a -> b -> c type Vec b = [b] instance Mul a b c => Mul a (Vec b) (Vec c) where ... f b x y = if b then (*) x [y] else y For actual arguments of f, there is no issue whatsoever with decidability. The type checker in my brain uses unification, i.e. top-down. The type checker in GHC uses inference, i.e. bottom-up. Why inference potentially suffers from non-termination for this program, I understand. My question is this: Is there a reason why type checking in GHC is inference-only, as opposed to a meet-in-the-middle combination of unification and inference? Would the type checker use both unification and inference (let's say alternating evaluation of both), the number of programs for which termination can be guaranteed is considerably larger - if I'm not mistaken, but I may very well have gotten it wrong. Regards, Philip PS. I realize that for this dependent typing scenario is useless once Type Families are here. I can't wait for a GHC with TFs. I raise this question, simply to understand why inference was chosen exclusively.

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Generalized newtype deriving 6.6 vs. 6.8
by Twan van Laarhoven 05 Nov '07

05 Nov '07

Hello, I noticed there is a difference in generalized newtype deriving between 6.6 and 6.8. In GHC 6.4.1 the following: > {-# LANGUAGE GeneralizedNewtypeDeriving #-} > > import Control.Monad.Error > > newtype MyMonad m a = MyMonad (m a) > deriving (Monad, MonadError String) correctly gives a derived instance MonadError String m => MonadError String (MyMonad m) The new GHC 6.8.1 complains with: No instance for (MonadError String m) arising from the 'deriving' clause of a data type declaration at DeriveTest.hs:(5,0)-(6,36) Possible fix: add an instance declaration for (MonadError String m) When deriving the instance for (MonadError String (MyMonad m)) Generalizing the instance to MonadError e m => MonadError e (MyMonad m) works in both versions. Twan

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Help with Building on Mac OS X Leopard
by R Hayes 05 Nov '07

05 Nov '07

What resembles an old issue has reappeared when building HEAD on Leopard. The build of the stage two compiler fails with: ld: in /Users/rfh/3rdParty/builds/ghc-6.9.20071028/libraries/ haskell98/dist/build/libHShaskell98-1.0.1.a, archive has no table of contents This happens when the modify time on library is later than the timestamp on the library index. It's not an uncommon issue for building software on the Mac. The usual cause is builds that copy .a files and are unaware of this mac feature. Running ranlib on libHShaskell98-1.0.1.a file and resuming the make causes the build to continue until it gets to the next .a file. ld: in /Users/rfh/3rdParty/builds/ghc-6.9.20071028/libraries/array/ dist/build/libHSarray-0.1.a, archive has no table of contents It seems this problem has occurred before. My guess is that a work- around was put in place that no longer works on Leopard. I'm not sure exactly where to look in the Make system. Any pointers would be appreciated.

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testing docon-2.11
by Serge D. Mechveliani 04 Nov '07

04 Nov '07

People, can anybody, please, test docon-2.11 ? It resides in http://www.botik.ru/pub/local/Mechveliani/docon/2.11-pre/ It needs to download, unzip, install and run the test according to install.txt, communicate to me the result (together with the GHC and system specification). It is for ghc-6.8.1 and ghc-6.6.1 (down-porting to 6.6.1 is by deleting " , containers" from docon.cabal). I have tested it in Debian Linux. It needs testing, for example, under MacOS. Thank you in advance for your help. ----------------- Serge Mechveliani mechvel(a)botik.ru

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6.6.1 installlers
by Bulat Ziganshin 04 Nov '07

04 Nov '07

Hello glasgow-haskell-users, i've found that 6.6.1 downloading page ( http://haskell.org/ghc/download_ghc_661.html ) doesn't contain info about availability of Debian, Fedora and SUSE packages. is it possible to add it there? (also for other unices where such packages exist) the reason is that i distribute sources of my program and point users to this page for instructions on installing GHC. but it suggests to use generic linux package and don't tell anything about OS-specific packages. my users are not haskellers so they will be unable to find and install GHC package without knowing its exact name -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Too many local registers...
by Cristian Perfumo 03 Nov '07

03 Nov '07

Hi, I did some modifications to GHC in order to read hardware counters. Many programs are compiled successfully, but with one of them, I have a problem: Too many local registers allocated by gcc at .../ghc-6.6.1-modified/driver/mangler/ghc-asm line 1602, <INASM> line 304643. It's ghc 6.6.1 on an Itanium processor. Some suggestion? Thanks in advance for an answer. Cristian

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confusing GADT/scoped type variables behaviour
by Ganesh Sittampalam 02 Nov '07

02 Nov '07

Hi, I'm having some trouble writing code that uses GADTs. I finally got something that is portable between GHC 6.6 and 6.8, but I don't really understand what's going on, and I'm a bit unhappy with the number of type signatures required. I'll explain them with a series of cut-down examples below, so please forgive the gratuitous beta-redexes. My testing has been with GHC 6.6 and 6.8.0.20070921, but I believe from more limited testing that 6.6.1 behaves the same as 6.6. My first program works fine with both GHC 6.6 and 6.8: {-# OPTIONS_GHC -fglasgow-exts #-} module GADT where data C x y where C :: P x y -> C x x data P x y where P :: Q x y -> P x y data Q x y where Q :: Q x y data D x y where D :: C y z -> D x z f :: forall x y . D x y -> () f (D (C p)) | P q <- (\p -> p) p = case q of Q -> () {- end of program -} However, when I change it slightly to make the lambda expression inspect the structure of p: {-# OPTIONS_GHC -fglasgow-exts #-} module GADT where data C x y where C :: P x y -> C x x data P x y where P :: Q x y -> P x y data Q x y where Q :: Q x y data D x y where D :: C y z -> D x z f :: forall x y . D x y -> () f (D (C p)) | P q <- (\p@(P a) -> p) p = case q of Q -> () {- end of program -} it continues to work with 6.6, but 6.8 complains that q has a wobbly type and I should add a type annotation. So, I do so, also adding one to the original pattern for p otherwise my type variables aren't in scope: {-# OPTIONS_GHC -fglasgow-exts #-} module GADT where data C x y where C :: P x y -> C x x data P x y where P :: Q x y -> P x y data Q x y where Q :: Q x y data D x y where D :: C y z -> D x z f :: forall x y . D x y -> () f (D (C (p :: P w z))) | P q :: P w z <- (\p@(P a) -> p) p = case q of Q -> () {- end of program -} Fine with 6.8, but now 6.6 is unhappy. The type variable 'w' is actually the same as 'y', and 6.6 seems to have noticed this fact and says I should have given them the same name. So, I do so: {-# OPTIONS_GHC -fglasgow-exts #-} module GADT where data C x y where C :: P x y -> C x x data P x y where P :: Q x y -> P x y data Q x y where Q :: Q x y data D x y where D :: C y z -> D x z f :: forall x y . D x y -> () f (D (C (p :: P y z))) | P q :: P y z <- (\p@(P a) -> p) p = case q of Q -> () {- end of program -} Now 6.6 is happy. But 6.8 doesn't believe they are the same, and rejects it. I finally got it to work with both by removing the forall in the signature of f: {-# OPTIONS_GHC -fglasgow-exts #-} module GADT where data C x y where C :: P x y -> C x x data P x y where P :: Q x y -> P x y data Q x y where Q :: Q x y data D x y where D :: C y z -> D x z f :: D x y -> () f (D (C (p :: P y z))) | P q :: P y z <- (\p@(P a) -> p) p = case q of Q -> () {- end of program -} But, I don't really understand why this is so. I guess the 'y' in the outer signature is no longer a scoped type variable, so 6.6 doesn't complain, and is no longer the same as the inner 'y', so 6.8 doesn't complain, but it all feels a bit unsatisfactory. So, is there a good explanation of the errors from 6.8? Is 6.8 behaving as expected? Finally, ideally I'd like not to have any type signatures in the body of f - is this feasible with 6.8 like it was with 6.6? Cheers, Ganesh

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