August 2005 - Haskell

Haskell-mode 2.0
by Stefan Monnier 02 Feb '09

02 Feb '09

I have recently taken over maintainership of Haskell-mode, and after making a bunch of changes, I figured it would be a good idea to make a new release. You can find this new release at: http://www-perso.iro.umontreal.ca/~monnier/elisp/ If you think it should also be found at http://www.haskell.org/haskell-mode/, then please tell John Peterson to get back to me (my email to him seem to go straight to the bitbucket. John?). This release has several changes that have all been only lightly tested, especially w.r.t compatibility with various Emacsen. See appended the NEWS file that describes some of the notewirthy changes. Stefan Changes since 1.45: * keybindings C-c <char> have been replaced by C-c C-<char> so as not to collide with minor modes. * The following modules are now automatically activated without having to add anything to haskell-mode-hook: haskell-font-lock (just turn on global-font-lock-mode). haskell-decl-scan (just bind `imenu' to some key). * In recent Emacsen, haskell-doc hooks into eldoc-mode. * haskell-hugs and haskell-ghci are superceded by inf-haskell. * Indentation rules have been improved when using layout inside parens/braces. * Symbols like -> and \ can be displayed as actual arrows and lambdas. See haskell-font-lock-symbols. * Tweaks to the font-lock settings. Among other things paren-matching with things like \(x,y) should work correctly now. * New maintainer <monnier(a)gnu.org>.

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Mixing monadic and non-monadic functions
by Sean E. Russell 17 Sep '05

17 Sep '05

Hello, I posted this question to comp.lang.functional, and someone suggested that I try this group instead. I'm struggling with monads. Well, not monads themselves, but mixing them with non-monadic functions. Here's my base case: someFunc :: String -> IO [a] ... ax <- someFunc a bx <- someFunc b assertBool "fail" $ length ax == length bx I don't like the assignments; the typing is redundant, if I have a lot of asserts like this, and the "variables" are temporary. What I'd much rather have is: ... assertBool "fail" $ (length $ someFunc a) == (length $ someFunc b) which is more readable, to my eye. The only solution which has been suggested that may work is liberal use of the liftM variants, but this gets *really* tedious and obtuse. Is there an elegant way to do what I want to do, or am I stuck with procedural-style assignments and bunches of temp vars? Thanks! -- ### SER ### Deutsch|Esperanto|Francaise|Linux|XML|Java|Ruby|Aikido ### http://www.germane-software.com/~ser jabber.com:ser ICQ:83578737 ### GPG: http://www.germane-software.com/~ser/Security/ser_public.gpg

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ANNOUNCE: fps -- fast packed strings
by dons＠cse.unsw.edu.au 12 Sep '05

12 Sep '05

Hey. I've cabalised the FastPackedString module from darcs, used in h4sh, as the `fps' library. fps provides mmapped and malloc'd packed strings (byte arrays held by a ForeignPtr), along with a list interface to these strings. It lets you do extremely fast IO in Haskell. For example, the shell identity function written in Haskell (i): $ time cat 200M > /dev/null 0.00s user 0.19s system 2% cpu 6.481 total $ time i 200M > /dev/null 0.00s user 0.00s system 0% cpu 0.172 total $ time cat 200M > /tmp/f 0.00s user 0.38s system 1% cpu 27.932 total $ time i 200M > /tmp/f 0.00s user 0.48s system 7% cpu 6.454 total The FastPackedString module was originally written by Bryan O'Sullivan, it was rewritten to use UArray by Simon Marlow, then rewritten and extended to support slices, mmapping, ForeignPtrs and lots of other stuff by David Roundy and the darcs team. This version fixes a couple of bugs related to conformance to List, adds a testsuite, and makes the code conveniently available as a cabalised library. Get it: http://www.cse.unsw.edu.au/~dons/fps.html darcs get http://www.cse.unsw.edu.au/~dons/code/fps -- Don Stewart

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cannot compile ghc on Debian unstable
by Michael Vanier 06 Sep '05

06 Sep '05

Right now, the Debian unstable package for GHC 6.4 won't install due to some conflict with libgmp3 (the package maintainer has been notified). I tried to compile the sources from scratch but found out that GHC requires a previously-existing version of itself to compile. I have hugs working fine, but configuring using --enable-hc-boot --with-hc=/usr/bin/hugs doesn't work (the configure completes but the compile fails very quickly). Has anyone managed to get this working? I'm actually somewhat surprised that there isn't a bootstrap-from-gcc-only mode available like there is in ocaml; what are the issues? Thanks in advance, Mike

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ANNOUNCE: h4sh - Haskell functions for shell scripting
by dons＠cse.unsw.edu.au 04 Sep '05

04 Sep '05

h4sh -- Haskell functions for shell scripting Unix is all about programs that do one thing, and one thing well. Unfortunately, over time, the common unix text processing commands have become bloated and silly, with rather arbitrary features for programs that should have simple semantics (consider uniq and wc outputting leading space, or cut indexing fields from 1, just for starters). On the other hand Haskell has a powerful and beautiful List library for processing text as lists of strings. h4sh exposes the Haskell List library as a set of shell utilities. Utilising function composition via pipes, we can transparently program in Haskell, in the shell :) Commands are generated from a description of their type. Higher order functions like map are handled using runtime evaluation, provided by the hs-plugins System.Eval library, allowing arbitrary Haskell code to be provided as arguments to, for example, map and filter. A (contrived) example: take -n 100 f | id | map -e show.length | filter -e '/= "0"' | sort | reverse | head Get it: http://www.cse.unsw.edu.au/~dons/h4sh.html darcs get --partial http://www.cse.unsw.edu.au/~dons/code/h4sh -- Don Stewart

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How to use STArray?
by oleg＠pobox.com 31 Aug '05

31 Aug '05

Benjamin Franksen wrote: > On Thursday 25 August 2005 19:58, Udo Stenzel wrote: > > [...] you'll need a type signature somewhere to help ghc resolve > > the overloading of newArray and readArray, which is surprisingly > > tricky due to the "s" that must not escape. This works: > > > > compute :: Int -> Int > > compute n = runST ( do > > arr <- newArray (-1, 1) n :: ST s (STArray s Int Int) > > readArray arr 1 > > ) > I am fighting with a similar problem. I want to use STUArray but > without committing to a fixed element type. That problem has been addressed in a message http://www.haskell.org/pipermail/haskell-cafe/2004-July/006400.html which discussed several solutions. Given below is one of the solutions adjusted to fit the question of the original poster. His code is almost unchanged. It would havebeen nice if the GHC library supported the second solution, a class Unpackable. Currently there are instances of MArray (STUArray s) e (ST s) and IArray UArray e for exactly the same set of types `e'. Alas, that condition is not stated formally, so we cannot infer that MArray (STUArray s) e (ST s) holds whenever IArray UArray e does. > {-# OPTIONS -fglasgow-exts #-} > > module Foo where > > import Data.Array.Unboxed > import Data.Array.ST > import Control.Monad.ST > > data Allocator m i e = forall a. MArray a e m => > Allocator ((i, i) -> m (a i e)) > > > copy :: (MArray a e m, IArray b e) => > a Int e -> Int -> b Int e -> Int -> Int -> m () > copy dest destix src srcix cnt > | cnt <= 0 = return () > | otherwise = do > writeArray dest destix (src ! srcix) > copy dest (destix+1) src (srcix+1) (cnt-1) > append :: (IArray UArray e, STUGood e) => > UArray Int e -> UArray Int e -> Int -> UArray Int e > append x y low = > runST (case allcg of Allocator newArray_ -> > (do > z <- newArray_ (low,low+len x+len y) > copy z low x (first x) (len x) > copy z (low+len x) y (first y) (len y) > unsafeFreeze z)) > where > len = rangeSize . bounds > first = fst . bounds > > class STUGood e where > allcg::Ix i => Allocator (ST s) i e > > instance STUGood Bool where > allcg = Allocator (newArray_:: Ix i => (i,i) -> ST s (STUArray s i Bool)) > > instance STUGood Float where > allcg = Allocator (newArray_:: Ix i => (i,i)-> ST s (STUArray s i Float)) > > -- etc. > > test = > append (listArray (1,1) [True]) (listArray (1,1) [False]) 0

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Haskell CVS repository now hosted by Galois
by Andy Moran 31 Aug '05

31 Aug '05

The cvs.haskell.org CVS repository, previously hosted by OGI (on glass.cse.ogi.edu) is now being hosted by Galois. The new machine is a 3.0 GHz Pentium 4 running Debian Linux (sarge); it will be actively maintained by Galois. Requests for system help should be directed to haskell-cvs(a)galois.com. Some software packages (esp. cvs and OpenSSH) have been upgraded, so some system behaviors may differ from those on the old server -- but generally the new server is a drop-in replacement for the old one. If you were previously using 129.95.44.145 or glass.cse.ogi.edu to access the CVS repository, then you should switch to cvs.haskell.org. If you were already using cvs.haskell.org, then you shouldn't notice much of a change (beyond better service). Cheers, Andy -- Andy Moran Phone: 503.626.6616, x113 Galois Connections Inc. Fax: 503.350.0833 12725 SW Millikan Way, Suite #290 http://www.galois.com Beaverton, OR 97005 moran(a)galois.com

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Haskell Weekly News: August 30, 2005
by John Goerzen 31 Aug '05

31 Aug '05

Haskell Weekly News: August 30, 2005 Greetings, and thanks for reading the fifth issue of HWN, a weekly newsletter for the Haskell community. Each Tuesday, new editions will be posted (as text) to [1]the Haskell mailing list and (as HTML) to [2]The Haskell Sequence. 1. http://www.haskell.org/mailman/listinfo/haskell 2. http://sequence.complete.org/ HWN is 1 day late this week. Pesky Real Life (TM) interfered. Sorry about that. Hopefully this won't happen again. Also, anyone that wants to help edit HWN is welcome to do so. See the contributing section at the end. New Releases * FUSE bindings. David Roundy [3]announced bindings for FUSE, the Linux library that lets people develop a filesystem using userspace code. Isaac Jones also [4]mentioned Jeremy Bobbio's FUSE bindings. * FastPackedString (FPS) packaging. Donald Bruce Stewart has extraced the FastPackedString module from darcs and [5]produced a standalone package. It is useful for working with binary data and blocks of string data. * Haskell Server Pages (HASP). Lemmih [6]announced Haskell Server Pages 0.3, an infrastructure for developing dynamic web sites. It's based around XML and the earlier work on HSP. * Cairo bindings for gtk2hs completed. Paolo Martini [7]announced that the Cairo bindings have been checked into the gtk2hs CVS repo on SourceForge. 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/8110 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/8125 5. http://article.gmane.org/gmane.comp.lang.haskell.general/12003 6. http://thread.gmane.org/gmane.comp.lang.haskell.general/12002 7. http://sourceforge.net/mailarchive/forum.php?thread_id=8063084&forum_id=442… Discussion Parsing Binary Files. Joel Reymont began an [8]interesting discussion by asking about using Haskell to implement a parser for a binary poker protocol. Erlang has some binary pattern matching features, and there was some discussion about achieving similar results in Haskell. 8. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/8111 Using STArray. Alistair Bayley asked how to use STArray to improve the performance of a program. Numerous suggestions were offered in the ensuing [9]discusion, including a link to some [10]examples on the Haskell wiki. 9. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/8091 10. http://haskell.org/hawiki/ImperativeHaskell Compiling Windows GUI Executables. Juan Carlos Arevalo Baeza [11]asked about compiling Windows GUI executables with ghc. Duncan Coutts posted a [12]link to the Gtk2Hs FAQ explaining the procedure. 11. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/8584 12. http://haskell.org/gtk2hs/archives/2005/06/23/hiding-the-console-on-windows/ Quotes of the Week Then Edsger Dijkstra came down from Mt. Sinai with a tablet proclaiming "Thou shalt not use GOTO; it is considered harmful"... From Chad Scherror on the haskell-cafe list: "I've been amazed at the level of effort put forth by the Haskell community as a whole to help out newcomers." About Haskell Weekly News Want to continue reading HWN? Please help us create new editions of this newsletter. Please see the [13]contributing information, or send stories to hwn -at- complete -dot- org. There is also a Darcs repository available. 13. http://sequence.complete.org/hwn-contrib

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Re: [Haskell-cafe] Monadic vs "pure" style (was: pros and cons of sta tic typing and side effects)
by Wolfgang Jeltsch 30 Aug '05

30 Aug '05

Am Dienstag, 30. August 2005 13:13 schrieb Bayley, Alistair: > [...] > I was also wondering what the disadvantages of monadic style are? Are there > compiler optimisations which are not possible with monadic code? State or StateT are monads which are implemented using ordinary pure Haskell. So, at least in the case of these two monads, you probably will enjoy the full power of optimizing. :-) Certain ST actions are implemented in Haskell, using lower level features, so certain optimizations should happen here as well. > Alistair. Best wishes, Wolfgang

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Re: [Haskell] Who brought the monad to us?
by Wolfgang Jeltsch 30 Aug '05

30 Aug '05

Am Dienstag, 30. August 2005 12:12 schrieben Sie: > Wolfgang [and Phil] > > As others have noted, Moggi had the key idea of using monads to support > the semantics of programming languages. Wadler was clearly the first to > have the amazing insight that monads could be a *programming* idiom too, > and gave several examples of their use, including lists, state monads, > continuations, and exceptions I believe. I was working with Phil at > Glasgow at the time, and I think I may have been the one to suggest > taking a monadic approach to *I/O* and FFI. But that's unimportant: > what is certain is that our co-authored paper in POPL'93 was the first > time the idea was published. > > Simon Hello Simon, thank you for your answer. Were you also the first one who had the idea to use monads for mutable variables and mutable arrays? Best wishes, Wolfgang

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