October 2010 - Glasgow-haskell-users

network programming with GHC 7
by Kazu Yamamoto 31 Oct '10

31 Oct '10

Hello, When I compiled a network server with GHC 7 without the "-threaded" option and ran it, I got the following error. file descriptor 5496824 out of range for select (0--1024). I have read the paper "Scalable Event Handling for GHC" and understand that this new IO manger assumes the "-threaded" option. Does this mean that we need the "-threaded" option to GHC 7 for networking programming and GHC 7 does not maintain backward compatibility? If so, this should be documented. --Kazu

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newbie: how to expose a package?
by Larry Evans 28 Oct '10

28 Oct '10

With the following .hs: ==<--TestPrettyPrintLeijen.hs--> module TestPrettyPrintLeijen where -- import Text.PrettyPrint.Leijen {- Above import causes error message: TestPrettyPrintLeijen.hs:3:7: Could not find module `Text.PrettyPrint.Leijen': Use -v to see a list of the files searched for. -} import Debug.QuickCheck.Batch {- Above import based on exposed-modules: section of: /usr/lib/ghc-6.12.1/package.conf.d/QuickCheck-1.2.0.0.conf However: ghci TestPrettyPrintLeijen.hs produces error: TestPrettyPrintLeijen.hs:9:7: Could not find module `Debug.QuickCheck.Batch': It is a member of the hidden package `QuickCheck-1.2.0.0'. Use -v to see a list of the files searched for. -} import GHC.Paths {- Above import based on exposed-modules: section of: http://hackage.haskell.org/packages/archive/ghc-paths/0.1.0.8/ghc-paths.cab… -} ==</--TestPrettyPrintLeijen.hs--> ghc still fails to find the QuickCheck as shown by: ==<--ghci run--> $ sudo ghc-pkg expose QuickCheck-1.2.0.0 $ ghci TestPrettyPrintLeijen.hs GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. TestPrettyPrintLeijen.hs:9:7: Could not find module `Debug.QuickCheck.Batch': It is a member of the hidden package `QuickCheck-1.2.0.0'. Use -v to see a list of the files searched for. Failed, modules loaded: none. Prelude> ==</--ghci run--> How does one enable import of a module from some package? TIA. -regards, Larry

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Unaligned word-sized reads on ByteArray#
by Johan Tibell 27 Oct '10

27 Oct '10

Hi, I noticed that indexWordArray# only allows for aligned reads (by forcing the offset to be in words, rather than in bytes.) Is it possible to perform unaligned reads on a ByteArray# e.g. going via Addr#? There's the byteArrayContent# primitive but I don't know how to force the ByteArray# to stay pinned in memory while performing my reads. The ByteArray# is not guaranteed to be pinned in my case. A somewhat related question: are there any defines (in e.g. MachDeps.h) that I could use to detect whether the machine supports unaligned reads? For example, if I knew the processor architecture, I could figure that out. Johan

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Re: Proposal: Require OverlappingInstances for the most specific instance only
by Christian Höner zu Siederdissen 26 Oct '10

26 Oct '10

Hi, can't remember to have been hit by it; but changing would mean that library maintainers can act more conservatively. Otherwise one needs to be able to guess if an instance might be overlapped. The new version wouldn't require that, yes? Gruss, Christian * John Smith <voldermort(a)hotmail.com> [26.10.2010 21:45]: > In the case of overlapping instance declarations, GHC currently > requires the less specific instance to be compiled with > OverlappingInstances for the more specific instance to be usable. > This means that, for example, if you write > > type ChessBoard = Array (Int,Int) Piece > > there is no way to > > instance Show ChessBoard where > show board = ... > > because Array is already an instance of Show, and was not compiled with OverlappingInstances. > > http://hackage.haskell.org/trac/ghc/ticket/3877 requests that > OverlappingInstances be required for only the most specific instance > declarations, as suggested in the documentation. "Perhaps the rule > should instead say that the overlapping instance declaration should > be compiled in this way, rather than the overlapped one ... We are > interested to receive feedback on these points." > > SPJ offered to make this change, if the list users agree. (See > comment 6.) Proposed deadline for discussion is 16th November. > > _______________________________________________ > Glasgow-haskell-users mailing list > Glasgow-haskell-users(a)haskell.org > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users

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Implicit 'forall' in data declarations
by Sebastian Fischer 25 Oct '10

25 Oct '10

Hello, GHC 6.12.3 allows to omit the explicit quantification of higher-rank type variables using 'forall' in data types if they appear in a type class context {-# LANGUAGE RankNTypes #-} data Foo = Foo (Eq a => a) Is this implicit introduction of 'forall' intended? If it is, why does it not work in function types? The following is not accepted by my GHC: bar :: Eq b => (Eq a => a) -> b bar x = x The error message is All of the type variables in the constraint `Eq a' are already in scope (at least one must be universally quantified here) (Use -XFlexibleContexts to lift this restriction) Using `FlexibleContexts` the signature of `bar` seems to be interpreted as bar :: (Eq b, Eq a) => a -> b because then the error becomes Couldn't match expected type `b' against inferred type `a' So unlike in data-type declarations, a 'forall' in a function type must be written explicitly even if the quantified variable appears in a local type class constraint. bar :: Eq b => (forall a . Eq a => a) -> b bar x = x I have not yet installed GHC 7. Is this inconsistency between data and function declarations intended or has it been changed in the new type checker? Sebastian

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ghc7 typing problem
by Christian Maeder 25 Oct '10

25 Oct '10

Hi, I've looked at: http://hackage.haskell.org/trac/ghc/blog/LetGeneralisationInGhc7 but still have a problem with the attached program that fails with: GHCi, version 7.1.20101010: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. [1 of 1] Compiling Main ( HasKey.hs, interpreted ) HasKey.hs:17:10: Couldn't match type `key' with `key1' because this skolem type variable would escape: `key1' This skolem is bound by the instance declaration In the instance declaration for `Ord (Keyed x)' at the final instance for Ord. The original code comes from http://hackage.haskell.org/packages/archive/uni-util/2.2.0.0/doc/html/Util-… Cheers Christian

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ANNOUNCE: GHC 7.0.1 Release Candidate 1
by Ian Lynagh 25 Oct '10

25 Oct '10

We are pleased to announce the first release candidate for GHC 7.0.1: http://new-www.haskell.org/ghc/dist/7.0.1-rc1/ This includes the source tarball, installers for OS X and Windows, and bindists for amd64/Linux and i386/Linux. Please test as much as possible; bugs are much cheaper if we find them before the release! Thanks Ian, on behalf of the GHC team

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GHC static binaries with glibc-2.12?
by Alexander Dunlap 23 Oct '10

23 Oct '10

Hi all, I recently upgraded my Arch Linux system to glibc 2.12 and static binaries compiled with GHC 6.12.3 all fail with the message "mkTextEncoding: invalid argument (Invalid argument)". This did not happen with glibc 2.11. Has anyone else had this problem? Does anyone have any advice for debugging it? Thanks, Alex

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Re: clearing GHCi (and, by extension, hint) loaded module dependencies
by Alex Suraci 23 Oct '10

23 Oct '10

On Tue, Sep 21, 2010 at 10:30 AM, Daniel Gorín <jcpetruzza(a)gmail.com> wrote: > Hi > > What I make of this is that you should run a new interpreter (i.e. use runInterpreter(T)) instead of calling reset. > > Could you try this this approach and see if it works? > > Daniel Every "load:" call already runs its own interpreter. I guess the session is sticking around somewhere in-between. I've been playing around with hint and the GHC API trying to figure this one out (with Simon's tips in mind), but haven't found a way to discard the session, or even on what level that should be done. In runInterpreter? Or in separate runGhc calls? The best guess I have so far is using getSession/setSession inside the interpreter call to restore it to the way it was before, but that seems to have no effect. Here's what I'm using to test: http://hpaste.org/40015/hintghc_memory Even with setSession, the cache seems to be sticking around - subsequent loads are faster, and the memory usage doesn't go down. -- Alex

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ghc-6.12.3 package base - build failure on ubuntu10.10 (works with 10.4)
by Mischa Dieterle 19 Oct '10

19 Oct '10

Hi, I'm getting a build failure when I try to compile ghc-6.12 from the http://darcs.haskell.org/ghc-6.12 repo. ---- ghc-cabal: Missing dependency on a foreign library: * Missing C library: iconv This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. make[1]: *** [libraries/base/dist-install/package-data.mk] Error 1 make: *** [all] Error 2 ---- I'm using a ubuntu 10.10-64 bit system with libc-bin and libc-dev-bin installed. I don't think the problem is a missing iconv library. Maybe the problem is in the generated configure script by the new autoconf version (autoconf version is 2.67). Maybe someone can help. Cheers, Mischa Stderr output of ./configure on base module is: ./configure: line 8709: ${ac_cv_search_iconv_t_cd_ ______________________cd___iconv_open_____ ______________________iconv_cd_NULL_NULL_NULL_NULL__ ______________________iconv_close_cd__+set}: bad substitution ./configure: line 8735: ac_cv_search_iconv_t_cd_: command not found ./configure: line 8736: ______________________cd___iconv_open_____: command not found ./configure: line 8737: ______________________iconv_cd_NULL_NULL_NULL_NULL__: command not found ./configure: line 8742: ${ac_cv_search_iconv_t_cd_ ______________________cd___iconv_open_____ ______________________iconv_cd_NULL_NULL_NULL_NULL__ ______________________iconv_close_cd__+set}: bad substitution ./configure: line 8742: ${ac_cv_search_iconv_t_cd_ ______________________cd___iconv_open_____ ______________________iconv_cd_NULL_NULL_NULL_NULL__ ______________________iconv_close_cd__+set}: bad substitution ./configure: line 8746: ${ac_cv_search_iconv_t_cd_ ______________________cd___iconv_open_____ ______________________iconv_cd_NULL_NULL_NULL_NULL__ ______________________iconv_close_cd__+set}: bad substitution ./configure: line 8746: ac_cv_search_iconv_t_cd_: command not found ./configure: line 8747: ______________________cd___iconv_open_____: command not found ./configure: line 8748: ______________________iconv_cd_NULL_NULL_NULL_NULL__: command not found ./configure: line 8751: ______________________cd___iconv_open_____: command not found

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