November 2001 - Haskell

GHC version 5.02.1 is released
by Julian Seward (Intl Vendor) 05 Nov '01

05 Nov '01

GHC 5.02.1 is available. Currently the source, x86-linux and sparc-solaris tarballs are available. We hope to add binary builds for Win32 and Alpha early next week. -- J The (Interactive) Glasgow Haskell Compiler -- version 5.02.1 ============================================================== We are pleased to announce a new patchlevel release of the Glasgow Haskell Compiler (GHC), version 5.02.1. The source distribution is freely available via the World-Wide Web, under a BSD-style license. See below for download details. Pre-built packages for Linux, FreeBSD, Solaris and Win32 are also available. Haskell is a standard lazy functional programming language; the current language version is Haskell 98, agreed in December 1998. GHC is a state-of-the-art programming suite for Haskell. Included is an optimising compiler generating good code for a variety of platforms, together with an interactive system for convenient, quick development. The distribution includes space and time profiling facilities, a large collection of libraries, and support for various language extensions, including concurrency, exceptions, and foreign language interfaces (C, C++, whatever). A wide variety of Haskell related resources (tutorials, libraries, specifications, documentation, compilers, interpreters, references, contact information, links to research groups) are available from the Haskell home page at http://www.haskell.org/ GHC's Web page lives at http://www.haskell.org/ghc/ What's new in 5.02.1 ====================== Fixed various bugs, some of which caused GHCi to crash or misbehave. Some documentation fixes. Nothing major. What's new in 5.02 ==================== 5.02 incorporates many small refinements and bug fixes over the previous stable release (5.00.2). There are no major changes. - Much improved support for Windows platforms. Binary builds are now entirely freestanding. There's no need to install Cygwin or Mingwin to use it. It's a one-click-install-and-off-you-go story now. - Several small changes to bring GHC into line with the newest Haskell 98 report. - GHCi (the interactive system) now works on Windows. - Partial FFI support in GHCi. At the moment, foreign import (both static and dynamic) is supported on x86 and sparc platforms. - A compacting garbage collector, to try and reduce space use. - Experimental: partial support for hierarchical module names. - Experimental: following heroic hacking by Ken Shan, 5.02 now works on Alpha (Tru64 only). Many 64-bit bugs have been shaken out. At the moment only the batch-mode compiler works -- no GHCi or native code generator yet. We've found and fixed more bugs than you could possibly imagine. A big thank-you to all those who reported bugs in the 5.00.X series. We claim to have fixed almost all reported bugs. In general we've spent a large amount of effort trying to improve the stability of the system relative to 5.00.X. (Famous last words ...) For full details see the release notes: http://www.haskell.org/ghc/docs/5.02/set/release-5-02.html How to get it =============== The easy way is to go to the WWW page, which should be self-explanatory: http://www.haskell.org/ghc/ We supply binary builds in the native package format for various flavours of Linux and BSD, and in InstallShield form for Windows folks. Everybody else gets a .tar.gz which can be installed where you want. Once you have the distribution, please follow the pointers in the README file to find all of the documentation about this release. On-line GHC-related resources =============================== Relevant URLs on the World-Wide Web: GHC home page http://www.haskell.org/ghc/ Haskell home page http://www.haskell.org/ comp.lang.functional FAQ http://www.cs.nott.ac.uk/~gmh/faq.html System requirements ===================== To compile programs with GHC, you need a machine with 64+MB memory, GNU C and perl. This release is known to work on the following platforms: * i386-unknown-{linux,freebsd,mingw32} * sparc-sun-solaris2 * alpha-dec-osf3 Ports to the following platforms should be relatively easy (for a wunderhacker), but haven't been tested due to lack of time/hardware: * hppa1.1-hp-hpux{9,10} * i386-unknown-solaris2 * mips-sgi-irix{5,6} * {rs6000,powerpc}-ibm-aix The builder's guide included in distribution gives a complete run-down of what ports work; an on-line version can be found at http://www.haskell.org/ghc/docs/5.02/building/building-guide.html Mailing lists =============== We run mailing lists for GHC users and bug reports; to subscribe, use the web interfaces at http://www.haskell.org/mailman/listinfo/glasgow-haskell-users http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs There are several other haskell and ghc-related mailing lists on www.haskell.org; for the full list, see http://www.haskell.org/mailman/listinfo/ Please report bugs using our SourceForge page at http://sourceforge.net/projects/ghc/ or send them to glasgow-haskell-bugs(a)haskell.org. GHC users hang out on glasgow-haskell-users(a)haskell.org. Bleeding edge CVS users party on cvs-ghc(a)haskell.org.

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Haskell 98 Revised
by Simon Peyton-Jones 05 Nov '01

05 Nov '01

Haskellers! It's that time of the month. I'm putting out the November release of the Revised Haskell 98 Report. As ever, I earnestly seek your feedback. Especially I'd like to know whether I have stumbled in rewriting the section about Enum in the light of recent email. http://research.microsoft.com/~simonpj/haskell98-revised My plan is to iterate just once more (early Dec), and then freeze the report at Christmas. I'm getting tired! Simon

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Re: Haskell 98 Revised
by Ian Lynagh 05 Nov '01

05 Nov '01

On Mon, Nov 05, 2001 at 06:47:17AM -0800, Simon Peyton-Jones wrote: > indeed, it's a stream of lexemes that gets passed to L, so > there's no whitespace anyway The report says: The input to L is: * A stream of tokens as specified by the lexical syntax in the Haskell report, with the following additional tokens: immediately before where I suggested "token" be changed to "lexeme". I think I prefer this for a descriptive algorithm as it means you can do things like the figures in section 2.7 (Layout). > | L (t:ts) ms = L ts ms if t is whitespace Bah, I *really* meant L (t:ts) ms = t : L ts ms if t is whitespace :-) Also, the line L (}:ts) (0:ms) = } : (L ts ms) should be L (}:ts) (m:ms) = } : (L ts ms) if m == 0 = error "Implicit block explicitly closed" otherwise or the } will get allowed through by L (t:ts) ms = t : (L ts ms) So my complete suggested function is: L (t:ts) [] = t : L ts [] if t is whitespace = error "lexeme outside of module contents" otherwise L ({n}:ts) (m:ms) = { : (L ts (n:m:ms)) if n > m = { : } : (L ts (m:ms)) otherwise L (<n>:ts) (m:ms) = ; : (L ts (m:ms)) if m = n = } : (L (<n>:ts) ms) if n < m = L ts (m:ms) otherwise L (t:ts) (m:ms) = } : (L (t:ts) ms) if m /= 0 and parse-error(t) L (}:ts) (m:ms) = } : (L ts ms) if m == 0 = error "Implicit block explicitly closed" otherwise L ({:ts) ms = { : (L ts (0:ms)) L (t:ts) ms = t : (L ts ms) L [] [0] = [] L [] (m:ms) = } : L [] ms if m /= 0 Thanks Ian

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RE: Haskell 98 Revised
by Simon Peyton-Jones 05 Nov '01

05 Nov '01

Gentle Haskellers Yes! The layout rule bites again. Ian writes: | Finally, ghci, hi and hugs seem to accept | | > module Foo where | > instance Fractional Int where | > foo = 5 In fact, GHC and Hugs have different interpretations: Hugs treats the 'foo' as part of the 'where', whereas GHC does not. Meanwhile the current draft of the report seems just wrong. The annotated program is: module Foo where {1} <1> instance Fractional Int where {1} <1> foo = 5 So when the algorithm hits the {1} on line 2, no case matches except the catch-all case, so {1} makes it through into the output, which is A Bad Thing. None of these pseudo-lexemes should get through to the output. The "obvious" result is: module Foo where { instance Fractional Int where {} ; foo = 5 } To fix this, it seems to me that all we need do is to add the following second clause to L L ({n}:ts) (m:ms) = { : (L ts (n:m:ms)) if n > m, (Note 3) = { : } : L ts (m : ms) otherwise This makes sure that the {n} case always has an outcome, and implicitly inserts { } where the layout does not increase. This is an old chestnut, but all the more reason for knocking it on the head (to mix metaphors). Simon

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RE: Haskell 98 Revised
by Simon Peyton-Jones 05 Nov '01

05 Nov '01

| http://research.microsoft.com/~simonpj/haskell98-revised/haskell98-repor t-html/index.html | says "Revised: October 2001" - am I seeing the latest version? Yes you are -- my mistake. | You still have | lexeme -> ... | qop | ... | in the lexical syntax but have | qop -> qvarop | qconop | in the context-free syntax - is this deliberate? It really sucks IMO. Your message about this is still in my "to deal with" pile. Last time I looked I didn't see an obvious solution, but now I look again, it seem simple. (Procrastination sometimes works.) Proposal: in the syntax for "lexeme", replace "qop" by "qvarsym | qconsym". So the syntax for lexeme becomes lexeme -> qvarid | qconid | qvarsym | qconsym | literal | special | reservedop | reservedid I think this restores the stratification between the lexical structure (no whitespace allowed) and the syntactic structure (whitespace allowed between lexemes). It also makes the syntax for "lexeme" look more symmetrical. Do you agree? Simon

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Type checking question
by Adrian Hey 05 Nov '01

05 Nov '01

Hello, I've been playing around with GTK+HS recently. This makes extensive use of Haskell classes, so I sometimes get strange type errors like this one.. textNew (creates a new text widget) has type: textNew :: AdjustmentClass adj => Maybe adj -> Maybe adj -> IO Text But when I try to create one using: txt <- textNew Nothing Nothing GHC complains: Main.hs:82: Ambiguous type variable(s) `a' in the constraint `GtkAdjustment.AdjustmentClass a' arising from use of `textNew' at Main.hs:82 in a `do' expression pattern binding: txt <- textNew Nothing Nothing My first thought was that I need a type signature for txt, but seeing as txt has to be type IO Text, I dont think that's possible (because 'adj' is not referenced). Is that correct? So, what should one do in this situation? Something like this perhaps.. myNothing :: Maybe dummyAdjustmentClassInstance myNothing = Nothing txt <- textNew myNothing myNothing I'm pretty sure that would do it, but it seems like an ugly solution. Is there a better way? Thanks -- Adrian Hey

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readFile
by bracaman＠box.sk 04 Nov '01

04 Nov '01

Hello all. It's me again :) This time I'd like to ask someone to explain me why this happens. I have this piece of code: test = do writeFile "/tmp/hsout" "first" h <- readFile "/tmp/hsout" writeFile "/tmp/hsout" "second" putStr h So, when i've done this i thought that (putStr h) would print the string "first". But it didn't, it printed the string "second". My question is why? And how can i do to print the first string instead of the first one. Thank you, Jo�o ------------------------------------ geek code inside :: powered by linux

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Re: URGENT: File exists
by Ashley Yakeley 03 Nov '01

03 Nov '01

At 2001-11-03 02:56, bracaman(a)box.sk wrote: >I need to create a function that checks if a file exists. My intention is >to do something like: > > teste :: String -> Bool (Beeing the String the FilePath) This cannot be done safely. Consider making a function with type test :: String -> IO Bool ... -- Ashley Yakeley, Seattle WA

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ANNOUNCE: HXML 0.1, an(other) XML parser for Haskell
by Joe English 02 Nov '01

02 Nov '01

2 Nov 2001 Announcing HXML, an(other) XML parser for Haskell. This implementation should have better space behaviour than HaXml's parser, and may be used as a drop-in replacement in existing HaXml programs. HXML is available at: <URL: http://www.flightlab.com/~joe/hxml/ > The current version is 0.1, and is slightly post-alpha quality. Tested with GHC 5.02, NHC98 1.10, and various recent versions of Hugs. Please contact Joe English <jenglish(a)flightlab.com> with any questions, comments, or bug reports. --Joe English jenglish(a)flightlab.com

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Re: Scope of imported names
by Marcin 'Qrczak' Kowalczyk 02 Nov '01

02 Nov '01

Fri, 2 Nov 2001 09:30:37 -0800, Simon Peyton-Jones <simonpj(a)microsoft.com> pisze: > | They are also different in spirit from the rules for > | instance declarations in section 4.3.2 where the binding > | occurrences for the names of the methods must be qualified if > | the unqualified method name is not in scope. > I will therefore propose the following simplification: > > remove the stuff from 4.3.2 about having a qualified name > for the class method; after all, an instance declaration is > only *allowed* to have declarations for the class methods > > That would simplify the syntax, and make the language more consistent. > Any objections? I don't have a strong opinion in either way, ok for me to make this change, but I don't agree that it would be more consistent. Instances don't contain binding occurrences of method names! They are not exported from the module which contains the instance. Well, instances are exported semantically, but not names of methods. You can't have a fixity declaration there. You can't have a type signature, although it's sometimes written in a comment (perhaps it should be permitted?). It's true that it's unambiguous because of the class they are written in. And they syntactically looks like binding occurrences to create an illusion that it's overloading... But in fact they contribute code to the same function which happens to dispatch the implementation on the type it is used at. At least this is how I think about it. I've recently implemented a toy language where providing implementations of generic functions is done by executing a particular function, giving it three arguments: the generic function, the type, and the implementation. It's clearly not a binding occurrence - the function must have already existed before. Similarly in Haskell. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ QRCZAK

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