- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] building the unix package and cabal
by Thomas Schilling 06 Feb '08

06 Feb '08

I don't know. Maybe someone on @cafe can help. (I CC'd) On Feb 4, 2008 5:22 PM, Galchin Vasili <vigalchin(a)gmail.com> wrote: > I have the gmp shared objects installed, i.e. .so's. Does ghc require static > linking with .a archive files? > > > > > On 2/4/08, Thomas Schilling <nominolo(a)googlemail.com> wrote: > > This is the GNU Multi-Precision library. You have to install that > > separately, Cabal can't do that for you. You should use the redhat > > package manager to install it. HTH > > > > On Feb 4, 2008 4:43 PM, Galchin Vasili <vigalchin(a)gmail.com> wrote: > > > Hi Thomas, > > > > > > Have you tried to build this package yourself? I get a linker error > .. > > > unresolved symbol "gmp". > > > > > > Vasili > > > > > > > > > > > > > > > On 2/4/08, Thomas Schilling <nominolo(a)googlemail.com> wrote: > > > > Build-type: Configure means that *Cabal uses ./configure * to build > > > > the package. Nothing changes for you. Just use the usual: > > > > > > > > runhaskell Setup.hs configure --prefix=... [--user] > > > > runhaskell Setup.hs build > > > > runhaskell Setup.hs install > > > > > > > > or with cabal-install: > > > > > > > > cabal install unix > > > > > > > > 2008/2/4 Galchin Vasili <vigalchin(a)gmail.com>: > > > > > Hello, > > > > > > > > > > I have been trying to build the unix package on RedHat RHEL 5. > > > Over > > > > > the weekend I read through the Cabal documentation. The unix-2.2.0.0 > > > > > unix.cabal specifies the "build-type" attribute as "Configure". > Based on > > > > > Cabal doc, I should run ./configure. After this step then what? > Bottom > > > line > > > > > is how do I build the unix-2.2.0.0 package on RHEL 5? > > > > > > > > > > Thank you, Vasili > > > > > _______________________________________________ > > > > > Haskell-Cafe mailing list > > > > > Haskell-Cafe(a)haskell.org > > > > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > > > > > > > > > > > > > > > > > > >

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Minor issue with mapAccumR
by Cale Gibbard 05 Feb '08

05 Feb '08

I'm not sure whether this would be considered worth fixing right away, or if we should wait until some other major compatibility breaking language change to fix it, but it appears that somehow the parameters to the function passed to mapAccumR are flipped relative to their natural order. To show what I mean, here is some code: Prelude Data.List> mapAccumR (\x y -> (concat ["(f ",x," ",y,")"], concat ["(g ",x," ",y,")"])) "z" ["1","2","3"] ("(f (f (f z 3) 2) 1)",["(g (f (f z 3) 2) 1)","(g (f z 3) 2)","(g z 3)"]) You can see here that the list is flipped over in the process, even though the right fold structure is there, it ends up looking like a left fold over the reverse of the list. One would want the law: fst . mapAccumR f z = foldr (fst . f) z to be true, but instead we have: fst . mapAccumR (flip f) z = foldr (fst . f) z You can see that structurally if we flip the parameters in the above example: Prelude Data.List> mapAccumR (\y x -> (concat ["(f ",x," ",y,")"], concat ["(g ",x," ",y,")"])) "z" ["1","2","3"] ("(f 1 (f 2 (f 3 z)))",["(g 1 (f 2 (f 3 z)))","(g 2 (f 3 z))","(g 3 z)"]) I also have some diagrams on http://cale.yi.org/index.php/Fold_Diagrams (near the end) displaying the difference, and that's where I first noticed it. Are many people using mapAccumR? How much would it hurt to change it? - Cale

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Is Haskore dead?
by Maurício 05 Feb '08

05 Feb '08

Hi, I've just tried using Haskore (I use Ubuntu and GHC), with no success. Since Haskore was started a long time ago, but it's not yet cabalized, and the author's page can not be reached, I can't say for sure if it's still maintained. Does anybody know? Thanks, Maurício

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Adding gcc type options with cabal (e.g. -mno-cygwin)
by bbrown 05 Feb '08

05 Feb '08

Is there a way to pass misc options to the cabal, ghc process. I tried the following: extra-libraries: sqlite3 extra-lib-dirs: C:\cygwin\lib include-dirs: C:\cygwin\usr\include ghc-options: -mno-cygwin runhaskell Setup.lhs build --ghc-options=-mno-cygwin -v No dice, doesn't show up. -- Berlin Brown email: berlin-dot-brown-AT-gmail-dot-com http://botspiritcompany.com/botlist/

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RE: highlighting-kate - syntax highlighting library
by mgsloan 05 Feb '08

05 Feb '08

Awesome! It looks quite nice, though it takes ages to compile. Would this be suitable for a text editor? One issue with text editors is you don't want to reprocess the entire file for each highlight. This, combined with multi-line syntactic elements, such as multiline strings or comments, makes for a rather awkward combination. It becomes a bit harder to predict the scope, highlighting wise, of editing actions. It may not really be necessary to do this very well. I for one find it annoying when you introduce an opening/closing symbol, it freezes for an instant, and the highlighting of the rest of the document alternates... So perhaps it could check if you're introducting a multiline element at the end when navigating off, re-evaluate highlighting of the rest of the document. Regardless of if the library can handle the requirements of text-editing in its current state, it looks like it wouldn't be too hard to add. Most of the work has been done :) Thanks! -Michael Sloan http://mgsloan.nfshost.com > Hello all, > > I've been working on a source code syntax highlighting library. It is > now somewhat usable, and help would be welcome in testing it further, so > I'm making it publicly available: > > darcs get http://johnmacfarlane.net/repos/highlighting-kate > > Currently, the following languages are supported: > > Ada Asp Awk Bash Bibtex > C Cmake Coldfusion Commonlisp Cpp > Css D Diff Djangotemplate Doxygen > Dtd Erlang Fortran Haskell Html > Java Javadoc Javascript Json Latex > Lex LiterateHaskell Lua Makefile Matlab > Mediawiki Nasm Objectivec Objectivecpp Ocaml > Pascal Perl Php Postscript Prolog > Python Ruby Scala Scheme Sgml > Sql SqlMysql SqlPostgresql Tcl Texinfo > Xml Xslt Yacc > > The parsers for individual languages are automatically generated > from Kate syntax definitions. The xml files have been included > in the repository, together with the program that converts them to > Haskell modules. There's also a standalone program, Highlight, that > you can use to test the highlighting. (See README for instructions.) > > Bug reports and patches are welcome. Note that I don't want to make > any manual modifications to the generated modules in > Text/Highlighting/Kate/Syntax. Changes should be made either in the > source xml files or in the program ParseSyntaxFiles.hs that generates > these modules. > > John

5 5

A handy little consequence of the Cont monad
by Cale Gibbard 05 Feb '08

05 Feb '08

Hello, Today on #haskell, resiak was asking about a clean way to write the function which allocates an array of CStrings using withCString and withArray0 to produce a new with* style function. I came up with the following: nest :: [(r -> a) -> a] -> ([r] -> a) -> a nest xs = runCont (sequence (map Cont xs)) withCStringArray0 :: [String] -> (Ptr CString -> IO a) -> IO a withCStringArray0 strings act = nest (map withCString strings) (\rs -> withArray0 nullPtr rs act) Originally, I'd written nest without using the Cont monad, which was a bit of a mess by comparison, then noticed that its type was quite suggestive. Clearly, it would be more generally useful whenever you have a bunch of with-style functions for managing the allocation of resources, and would like to turn them into a single with-style function providing a list of the acquired resources. - Cale

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Bug in System.Environment - EOT inserted into argument string
by David Fox 05 Feb '08

05 Feb '08

I'm seeing the character ^D inserted into argument strings that are about 256 characters long with GHC 6.8.2. Anyone else? Test.hs: module Main where import System.Environment import System.IO main = do args <- getArgs hPutStrLn stderr ("args: " ++ show args) Output: $ ghc6 --make Test.hs -o test [1 of 1] Compiling Main ( Test.hs, Test.o ) Linking test ... $ ./test "012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789" args: ["01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234\EOT5678901234567890123456789"]

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Re: [Haskell-cafe] building the unix package and cabal
by Thomas Schilling 04 Feb '08

04 Feb '08

This is the GNU Multi-Precision library. You have to install that separately, Cabal can't do that for you. You should use the redhat package manager to install it. HTH On Feb 4, 2008 4:43 PM, Galchin Vasili <vigalchin(a)gmail.com> wrote: > Hi Thomas, > > Have you tried to build this package yourself? I get a linker error .. > unresolved symbol "gmp". > > Vasili > > > > > On 2/4/08, Thomas Schilling <nominolo(a)googlemail.com> wrote: > > Build-type: Configure means that *Cabal uses ./configure * to build > > the package. Nothing changes for you. Just use the usual: > > > > runhaskell Setup.hs configure --prefix=... [--user] > > runhaskell Setup.hs build > > runhaskell Setup.hs install > > > > or with cabal-install: > > > > cabal install unix > > > > 2008/2/4 Galchin Vasili <vigalchin(a)gmail.com>: > > > Hello, > > > > > > I have been trying to build the unix package on RedHat RHEL 5. > Over > > > the weekend I read through the Cabal documentation. The unix-2.2.0.0 > > > unix.cabal specifies the "build-type" attribute as "Configure". Based on > > > Cabal doc, I should run ./configure. After this step then what? Bottom > line > > > is how do I build the unix-2.2.0.0 package on RHEL 5? > > > > > > Thank you, Vasili > > > _______________________________________________ > > > Haskell-Cafe mailing list > > > Haskell-Cafe(a)haskell.org > > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > > > > >

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building the unix package and cabal
by Galchin Vasili 04 Feb '08

04 Feb '08

Hello, I have been trying to build the unix package on RedHat RHEL 5. Over the weekend I read through the Cabal documentation. The unix-2.2.0.0 unix.cabal specifies the "build-type" attribute as "Configure". Based on Cabal doc, I should run ./configure. After this step then what? Bottom line is how do I build the unix-2.2.0.0 package on RHEL 5? Thank you, Vasili

1 0

Circular enums
by Ben Butler-Cole 04 Feb '08

04 Feb '08

[Resend with formatting maybe fixed.] Hello I'm trying to define functions that allow you to traverse a bounded enumeration, "wrapping" at the start and the end. My implementation looks like this: next, prev :: (Enum a, Bounded a) => a -> a next = turn 1 prev = turn (-1) turn :: (Enum a, Bounded a) => Int -> a -> a turn n e = toEnum (add (fromEnum (maxBound::a) + 1) (fromEnum e) n) where add mod x y = (x + y + mod) `rem` mod Which fails to type check under GHC with this error: No instance for (Bounded a) arising from use of `maxBound' at Hbot.hs:6:34-41 Probable fix: add (Bounded a) to the expected type of an expression In the expression: maxBound :: a In the first argument of `fromEnum', namely `(maxBound :: a)' In the first argument of `(+)', namely `fromEnum (maxBound :: a)' My (clearly flawed) understanding of the signature I've specified for 'turn' means *exactly* that a is Bounded. Can anyone enlighten me as to where my understanding is going awry and how (whether) I can achieve what I'm trying to do. Thank you Ben

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ANN: heap-0.2
by Stephan Friedrichs 04 Feb '08

04 Feb '08

A flexible heap implementation supporting min-, max- and custom-ordered heaps. New features since version 0.1: - Foldable and Read instance - filter, partition - subrange functions: take, drop, splitAt, takeWhile, span, break http://hackage.haskell.org/cgi-bin/hackage-scripts/package/heap-0.2.1 //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr

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parsec3 pre-release [important note]
by Derek Elkins 04 Feb '08

04 Feb '08

I forgot to mention that the Text.Parsec modules should be preferred to the Text.ParserCombinators.Parsec modules as the Haddock documentation reveals.

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ANN: bimap 0.1 - a bidirectional map
by Stuart Cook 04 Feb '08

04 Feb '08

Data.Bimap is a data structure that represents a bidirectional mapping between two key types. A bimap has two type parameters; each value in the bimap is associated with exactly one value of the opposite type. In other words, it's a bijection between (subsets of) its argument types. The API is loosely based on Data.Map; feedback and suggestions are most welcome. So far I've only tested it on GHC 6.6 on Linux/x86, with Cabal 1.2.3.0. Let me know if it works or breaks on other configurations. Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bimap-0.1 Haddocks: http://code.haskell.org/~scook0/haddock/bimap/ Darcs: darcs get http://code.haskell.org/bimap Stuart Cook

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Cabal, GHC, FFI and Visual Studio on Windows
by Magnus Therning 04 Feb '08

04 Feb '08

Is it possible to get Cabal to use 'cl' (Microsoft's C/C++ compiler shipped with Visual Studio Express)? I've found the Wiki page on using Visual Studio to create a DLL, then convert it to a .a file so that GHC can consume it. I'd rather skip using Visual Studio to build things and just ship a Cabalised package. /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus．therning＠gmail．com http://therning.org/magnus What if I don't want to obey the laws? Do they throw me in jail with the other bad monads? -- Daveman

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Who started 42, and when?
by Anthony Clayden 04 Feb '08

04 Feb '08

The earliest use of 42 in English humour I know of is Lewis Carroll's "Hunting of the Snark", written 1874 when the author was aged 42. Wikipedia says it all, and refers to Martin Gardner's "The Annotated Snark" (which is excellent). Lewis Carroll is the pen name of Charles Dodgson - a mathematician/logician. Gardner is of course a mathematician/science writer with an interest in puzzles and paradoxes. So although both rather pre-date functional programming, I think we might say there's a similar streak of humour. Sadly, Douglas Adams never revealed what language 'Deep Thought' was programmed in, but perhaps the machine it was 'unworthy to design' was to run Haskell natively? Anthony > The arbitrary constant was made popular by Douglas Adams in > the mid-1970s radio series ``A Hitchhikers Guide to the Galaxy'' (a > trilogy in 4 parts) --- however it does have a basis in the standard > model of physics --- a paper in Phys.Rev. of the early 1970s > described the unification of the Electro-Weak and Strong nuclear > forces --- the arbitrary constant (of nearly) 42 appears in the > calculations. I forget the original paper but if you get hold of > Frank Close ``The Cosmic Onion'' a graph reproduces the result. I met > Douglas Adams once at a book signing and asked him how he got hold of > the Phys.Rev. paper so early. Technically he should have written that > ``42 is the answer to life, the universe and everything except for > gravity and a few other arbitrary constants'' > > Adams was interested in computing --- I think his reaction to being > told about functional programming was to wonder what non-functional > programming might be.

1 0

Who started 42, and when?
by Loup Vaillant 04 Feb '08

04 Feb '08

I have read quite a lot of Haskell papers, lately, and noticed that the number 42 appeared quite often, in informal tutorials as well as in very serious research papers. No wonder Haskell is the Answer to The Great Question of Life, The Universe, and Everything, but I would like to know who started this, and when. Google wasn't much help, and I can't believe it's coincidence --hence this email. I hope I didn't opened some Pandora box. :-) Cheers, Loup

10 12

Poor libraries documentation
by Neil Mitchell 04 Feb '08

04 Feb '08

Hi, I went looking for the the function in Haskell to calculate cos^{-1}, inverse cosine. Unfortunately, the poor documentation in the libraries hampered my attempts. The documentation for the trig functions in Haskell is completely non-existent: http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v%3Acos For a start, its probably a good idea to mention that cos is an abbreviation of cosine (most people will know, but its handy to state it). Secondly, and much more importantly, it should state whether these measurements are in degrees or radians. It should also state things like acos is the inverse of cos - its been a while since I last used trig and I had to look it up!!! We are also lacking documentation for things like odd/even, which are obvious enough, but its nice to say that they meet the intuition. Could haddock be extended to give a warning message (in -Wall mode perhaps) when an exported function has no comment associated with it? This would be a really nice project for someone to take on, and very much appreciated :-) Thanks Neil

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IRC Statistics
by Vlad Dogaru 04 Feb '08

04 Feb '08

Hello, as part of an effort to learn Haskell, me and a few friends want to write an IRC statistcs generator. It would analyse logs and output HTML, text, or whatever other format. However, I have a few questions; we're all pretty new to this and it would be a shame to start off terribly wrong and get bored before we get to the fun parts. 1. Is there a similar effort in Haskell? I've seen a truly awesome IRCStats, but written in C (not that that's a bad thing). 2. I was thinking of the following structure: * a uniform Event format: joins, parts, actions, normal lines, and everything about them: the user, date and time, etc. * functions that parse logs to a list of events. Exotic log format? Just write a different function! (whatever `exotic' may mean) * functions that do various statistics on a list of events. The output will not be uniform. Examples are: who spoke most, what time people speak most, etc. * some way to make these into a common output form, maybe every above module having two functions, one for `internal' format, and one for converting that to proper output. Now, there will probably be a lot of opportunities to ask for feedback on possible statistics and log formats. My (main) question is whether you see anything conceptually wrong in this approach. With a bit of luck, we will be announcing hirst-0.1 in a few weeks or months (we're doing this while having schoool and other engagements). Thank you for your time, Vlad PS: This is my first post here, please point out any inadequacy. -- There is nothing more dangerous than an idea when it is the only one you have.

1 0

ANN: strictify 0.1
by Sterling Clover 04 Feb '08

04 Feb '08

Dear Friend, Have you ever stared at a maze of Haskell code and thought "Gosh, I'm just feeling lazy today. Everything works, and I mainly understand the strictness characteristics of my program. But I just can't decide where to put those last few bangs. Maybe I don't need to micro-optimize anyway." Sure you have. It's ok. You can let it out. You're among friends here. Why, I bet you've even gone and sprinkled some bangs randomly, hoping for the best. We've all been there. Maybe you even got those pesky strictness annotations right, but a new version of GHC with its ever improving strictness analyzer came along and rendered some obsolete. And yet there they still lie, consuming whole tens of picoseconds worth of your hard-earned processor cycles and troubling your dreams. Well, friend, your dreams need be troubled no more. The time has come for a new era! The era of strictifiericization version 0.1. An era where you can kiss those micro-optimization troubles over silly shootout entries goodbye! Instead of brute-forcing your way through permutations of strictness entries let your computer do the work for you. That's why we invented them after all! Rather than putting "!" in just the right places, put "{- ! -}" in every place you _might_ want a strictness annotation. Then sit back, pop open a cool refreshing brew, and wait (and wait and wait) as strictify does the rest!* Available now now now at hackage: http://hackage.haskell.org/cgi-bin/ hackage-scripts/package/strictify-0.1 Darcs repository at: http://code.haskell.org/~sclv/strictify/ *To prevent exponential running time, strictify only produces a local rather than global optimum of strictness patterns, which should be sufficient in 99% of all cases. Strictify only works on POSIX- compliant systems. Strictify is currently only suitable for "shootout"-style executables which are contained in a single main file, accepting input from argv, stdin, or both. Strictify will not fully execute until it recieves an EOF in stdin. If you cannot produce an EOF through ctrl-D and are not streaming an input file in, you may be forced to run "echo "" | strictify". No guarantee is made, express or implied, as to strictify improving the speed of your program or your mental acuity regarding strictness. Offer void where prohibited. As strictify contains small parts, it is not suitable for children under the age of five. Do not ingest strictify more than seventy five times in a one hour period. If symptoms persist, consult your physician. --S

1 0

more haskeem: it's just scheme in haskell now, no more "almost"
by Uwe Hollerbach 04 Feb '08

04 Feb '08

Hello, haskellers, my mud pies are getting bigger: I have added an exception-handling mechanism to haskeem (ie, for handling exceptions at the scheme level, not the haskell level; that was already working), and also hooked up the REPL to gnu readline: the example code for the readline command was practically tailor-made for me! :-) Also, I must apologize: I screwed up the URL earlier: I had said http://www.korgwal.com/software/haskeem/ and then promptly went and stuck it into http://www.korgwal.com/haskeem/ ... you may attribute that to rapidly-advancing senility, if you like, I won't contradict you. Anyway, I've fixed it by simply putting copies into both places. regards, Uwe Hollerbach

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hdbc, Oracle, and Solaris
by Daniil Elovkov 04 Feb '08

04 Feb '08

Hello folks. I don't understand whether hdbc has a specific Oracle backend or not (not via odbc). It is listed in the description of hdbc, but not really found elsewhere, it seems. I'd like to have a non-odbc support because it is very desirable to have it working on Solaris, and I'm not sure if it will be easy to set it up with odbc there. So, the question might go: has somebody had success with native Oracle support on Solaris with hdbc? Well, or hsql?

1 0

Yi, or Gtk2hs or fedora rpm problem?
by Jon Fairbairn 04 Feb '08

04 Feb '08

This was mentioned on the yi-devel list <http://groups.google.com/group/yi-devel/browse_frm/thread/392c3cd612490b1a/…> but didn't cause much excitement as it's not clear whose problem it is, so I'll ask here as well: I recently downloaded yi-0.3 and tried to build it, but get Loading package base ... linking ... done. Loading package array-0.1.0.0 ... linking ... done. Loading package bytestring-0.9.0.1 ... linking ... done. Loading package regex-base-0.72.0.1 ... linking ... done. Loading package regex-posix-0.72.0.2 ... linking ... done. Loading package regex-compat-0.71.0.1 ... linking ... done. Loading package fingertree-0.0 ... linking ... done. Loading package mtl-1.1.0.0 ... linking ... done. Loading package glib-0.9.12.1 ... linking ... done. Loading package cairo-0.9.12.1 ... linking ... done. yi: /usr/lib/ghc/6.8.2/gtk2hs/HSgtk.o: unknown symbol `containerszm0zi1zi0zi1_DataziSequence_length_info' Loading package gtk-0.9.12.1 ... linking ... yi: exception :: GhcException for any attempted invocation of yi. I don't know whether this problem is specific to yi, to gtk2hs or to the fedora 8 rpm of gtk2hs or something else (ghc 6.8.2). I tried to rpm --rebuild the gtk2hs source rpm, but the build failed, complaining of missing documentation files (the spec file can't be right, or I'd have seen an unsatisfied build-dependency message instead). What's the next step? -- Jón Fairbairn Jon.Fairbairn(a)cl.cam.ac.uk

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SPJ on the radio (at .NET Rocks :)
by Don Stewart 04 Feb '08

04 Feb '08

Simon talks about laziness, purity and other FP concepts to some .NET guys. Simon starts 7minutes 20seconds in. http://www.dotnetrocks.com/default.aspx?ShowNum=310 Good work Simon! -- Don

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ANN: Hlist 0.1 on Hackage
by gwern0＠gmail.com 03 Feb '08

03 Feb '08

Hey everyone: I'd like to make a short announcement that with the permission of its maintainer, I've uploaded HList v0.1 to Hackage. You can find the Hackage page here: <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HList-0.1>. 'cabal install HList' should also work. HList for those who don't know is a sort of OO Haskell package which permits heterogeneous lists; you can find out more at <http://homepages.cwi.nl/~ralf/HList/>. (The Darcs repository is at <http://darcs.haskell.org/HList>.) What changes have been made to the darcs repo? Well, they are mostly updates and cleanups - I've updated build-depends for GHC 6.8.x; largely moved from -fglasgow-exts to LANGUAGE pragmas; put the modules in a proper module namespace; fixed up Haddock generation; removed some unused files, and other things of that nature. -- gwern Covert data bank Armani Larson Missiles Dick CTP SO13 AUTODIN

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Refactoring from State monad to ST monad, for STUArray
by Denis Bueno 03 Feb '08

03 Feb '08

Is it possible to use the ST monad as a (drop-in) replacement for the State monad in the following situation? If not, is there a "best practice" for refactoring? I have a bunch of functions that return state actions: type MyState = ... foo1 :: T1 -> State MyState a foo2 :: T2 -> State MyState a ... foon :: Tn -> State MyState a And I'd like to refactor this to use the ST monad, mechanically, if possible. All uses of the MyState inside State are single-threaded. In my application, MyState is a record with 5 or so fields. One of those fields uses a list to keep track of some information, and I'd like to change that to STUArray, because it changes my bottleneck operations from O(n) to O(1). This, of course, requires having the ST monad around, in order to achieve the proper time complexity. Is there an easy way to do this? In the future, should I *start out* with the ST monad if I suspect I'll need to use an imperative data structure for efficiency reasons? I started out with State because I'm modeling a transition system, so it seemed natural. Any advice is appreciated. -- Denis

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strange GHC assembler failure
by Tim Newsham 03 Feb '08

03 Feb '08

I'm getting a weird build error: [ 9 of 95] Compiling Plugin.Pl.Common ( Plugin/Pl/Common.hs, dist/build/lambdabot/lambdabot-tmp/Plugin/Pl/Common.o ) /tmp/ghc52608_0/ghc52608_0.s: Assembler messages: /tmp/ghc52608_0/ghc52608_0.s:36:0: Error: unassigned file number 1 [... more of these ...] I narrowed this down -- this happens when I add my new library "silc-client" to the "Build-depends:" line in the cabal file even if none of its code is referenced. Removing the dependency makes the error go away. The module I'm referencing is a new one I'm still working on and it makes use of FFI and references external headers and libraries. (I put a copy at http://www.thenewsh.com/~newsham/silc-client.tgz if it helps anyone debug.. this is not release-quality code though). Any idea what is going on here? Tim Newsham http://www.thenewsh.com/~newsham/

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Re: [Haskell-cafe] Circular enums
by Ben Butler-Cole 03 Feb '08

03 Feb '08

On Feb 2, 2008, at 18:41 , I wrote: > No instance for (Bounded a) > arising from use of `maxBound' at Hbot.hs:6:34-41 > (...) > My (clearly flawed) understanding of the signature I've specified > for 'turn' means *exactly* that a is Bounded. Brandon Allbery replied: > The problem is that the scope of a is the type signature; it does > *not* extend to the definition. > > You can try omitting the type on maxBound and minBound, or you > can enable the scoped type variables extension Thank you. This compiles fine with the Glasgow extensions turned on as long as the type in the function signature is universally quantified: turn :: forall a. (Enum a, Bounded a) => Int -> a -> a turn n e = toEnum (add (fromEnum (maxBound::a) + 1) (fromEnum e) n) where add mod x y = (x + y + mod) `rem` mod

1 0

Circular enums
by Ben Butler-Cole 03 Feb '08

03 Feb '08

Hello I'm trying to define functions that allow you to traverse a bounded enumeration, "wrapping" at the start and the end. My implementation looks like this: next, prev :: (Enum a, Bounded a) => a -> a next = turn 1 prev = turn (-1) turn :: (Enum a, Bounded a) => Int -> a -> a turn n e = toEnum (add (fromEnum (maxBound::a) + 1) (fromEnum e) n) where add mod x y = (x + y + mod) `rem` mod Which fails to type check under GHC with this error: No instance for (Bounded a) arising from use of `maxBound' at Hbot.hs:6:34-41 Probable fix: add (Bounded a) to the expected type of an expression In the expression: maxBound :: a In the first argument of `fromEnum', namely `(maxBound :: a)' In the first argument of `(+)', namely `fromEnum (maxBound :: a)' My (clearly flawed) understanding of the signature I've specified for 'turn' means *exactly* that a is Bounded. Can anyone enlighten me as to where my understanding is going awry and how (whether) I can achieve what I'm trying to do. Thank you Ben

2 1

Circular enums - resend
by Ben Butler-Cole 03 Feb '08

03 Feb '08

[Resending with formatting fixed.] Hello I'm trying to define functions that allow you to traverse a bounded enumeration, "wrapping" at the start and the end. My implementation looks like this: next, prev :: (Enum a, Bounded a) => a -> a next = turn 1 prev = turn (-1) turn :: (Enum a, Bounded a) => Int -> a -> a turn n e = toEnum (add (fromEnum (maxBound::a) + 1) (fromEnum e) n) where add mod x y = (x + y + mod) `rem` mod Which fails to type check under GHC with this error: No instance for (Bounded a) arising from use of `maxBound' at Hbot.hs:6:34-41 Probable fix: add (Bounded a) to the expected type of an expression In the expression: maxBound :: a In the first argument of `fromEnum', namely `(maxBound :: a)' In the first argument of `(+)', namely `fromEnum (maxBound :: a)' My (clearly flawed) understanding of the signature I've specified for 'turn' means *exactly* that a is Bounded. Can anyone enlighten me as to where my understanding is going awry and how (whether) I can achieve what I'm trying to do. Thank you Ben

1 0

weird behavior with FFI
by Tim Newsham 03 Feb '08

03 Feb '08

I am working on haskell bindings to C functions using FFI. I have a callback function that returns "IO ()". When I pass in the callback function: foo = printf "foo" it crashes (is there an easy way to debug this exception using ghc6.8.2?) bot: SilcClient_d1al: uncaught exception however, if I pass in the callback function: foo = do printf "foo" return () it does not crash. Is this a bug in my bindings? In ghc/ffi? Full code is at: http://www.thenewsh.com/%7Enewsham/silcbot.tgz Tim Newsham http://www.thenewsh.com/~newsham/

2 2

highlighting-kate - syntax highlighting library
by John MacFarlane 03 Feb '08

03 Feb '08

Hello all, I've been working on a source code syntax highlighting library. It is now somewhat usable, and help would be welcome in testing it further, so I'm making it publicly available: darcs get http://johnmacfarlane.net/repos/highlighting-kate Currently, the following languages are supported: Ada Asp Awk Bash Bibtex C Cmake Coldfusion Commonlisp Cpp Css D Diff Djangotemplate Doxygen Dtd Erlang Fortran Haskell Html Java Javadoc Javascript Json Latex Lex LiterateHaskell Lua Makefile Matlab Mediawiki Nasm Objectivec Objectivecpp Ocaml Pascal Perl Php Postscript Prolog Python Ruby Scala Scheme Sgml Sql SqlMysql SqlPostgresql Tcl Texinfo Xml Xslt Yacc The parsers for individual languages are automatically generated from Kate syntax definitions. The xml files have been included in the repository, together with the program that converts them to Haskell modules. There's also a standalone program, Highlight, that you can use to test the highlighting. (See README for instructions.) Bug reports and patches are welcome. Note that I don't want to make any manual modifications to the generated modules in Text/Highlighting/Kate/Syntax. Changes should be made either in the source xml files or in the program ParseSyntaxFiles.hs that generates these modules. John

1 0

Issues with hsql-sqllite build; errors from the hackage download
by bbrown 03 Feb '08

03 Feb '08

There seems to be an issue with the hsql-sqlite3. Anyone have a fix. Should I use what is from darcs? Index of /packages/archive/hsql-sqlite3/1.7/logs/failure The Glorious Glasgow Haskell Compilation System, version 6.8.1 $ runhaskell Setup.lhs configure Setup.lhs:7:33: Module `Distribution.Simple.Utils' does not export `rawSystemVerbose' -- Berlin Brown [berlin dot brown at gmail dot com] http://botspiritcompany.com/botlist/?

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Re: HList error with hFoldr
by oleg＠okmij.org 03 Feb '08

03 Feb '08

Denis Bueno wrote: > For the moment my HLists only contain Ints. ... > -- Why should the following generate an error? > testApplyDistSum = hFoldr ApplyDistSum 0 ((4,4) .*. hNil) Here is the problem: in Haskell, 4 is not an Int. (4::Int) is an Int, but just 4 is a _polymorphic_ constant of the type Num a => a. Because it is polymorphic and so does not have any defined type, the type checker cannot chose an appropriate instance for ApplyDistSum. The error message says this directly: > No instance for (Apply ApplyDistSum ((t, t1), r1) r) Note the appearance of lower-case identifiers t, t1, r1, and r in the error message. They stand for the types that the type checker cannot figure out. When you use hFoldr in a larger expression, the types often become constrained by other components of the expression and so type variables become instantiated. In the simple cases as above, there is no information available to instantiate the type variables, hence the error. You have to give the type-checker hints in the form of type annotations: testApplyDistSum = hFoldr ApplyDistSum (0::Int) ((4::Int,4::Int) .*. hNil) In general, it is possible to avoid the type annotation on the accumulator (in this case, 0). The type checker could figure out the type of the result. But that requires specifying functional dependencies. The type annotations might be easier to start with. Incidentally, it is generally a good idea in Haskell to write Int constants as (1::Int), explicitly specifying their type. Here's a bit elaborated example: {-# OPTIONS -fglasgow-exts #-} module B where import HList class (Num i) => MetricSpace e i where dist :: e -> e -> i instance Num i => MetricSpace Int i where x `dist` y = fromIntegral $ abs (y - x) instance Floating i => MetricSpace Float i where x `dist` y = realToFrac $ abs (y - x) data ApplyDistSum = ApplyDistSum instance (MetricSpace e r) => Apply ApplyDistSum ((e, e), r) r where apply _ (p, v) = v + uncurry dist p testApplyDistSum = hFoldr ApplyDistSum (0::Double) ((4::Int,5::Int) .*. hNil) testApplyDistSum1 = hFoldr ApplyDistSum (0::Double) ( (4::Float,5.1::Float) .*. (4::Int,5::Int) .*. hNil)

2 4

newbie q about types
by Logesh Pillay 02 Feb '08

02 Feb '08

I have a list. Each component is a list with 2 whole numbers. I want to multiply the second number by the log of the first eg tail ([519432,525806]) * log (head [519432,525806]). I get the ffg error message: No instance for (Floating [t]) arising from a use of `log' at <interactive>:1:25-50 Possible fix: add an instance declaration for (Floating [t]) In the second argument of `(*)', namely `log (head [519432, 525806])' In the expression: tail ([519432, 525806]) * log (head [519432, 525806]) In the definition of `it': it = tail ([519432, 525806]) * log (head [519432, 525806]) I've tried the only type signature I know "fromIntegral" but it does not help. How to fix? Thanks Logesh

3 2

parsec3 pre-release
by Derek Elkins 02 Feb '08

02 Feb '08

I'm currently getting Paolo Martini's Google Summer of Code project, an updated version of Parsec, into a releasable state, and I will be maintaining it for at least a while. Paolo's major additions are: * The Parser monad has been generalized into a Parser monad transformer * The parsers have been generalized to work over a stream of any type, in particular, with bytestrings. I have made a few minor additions as well: * There is Haddock documentation for almost all functions * The Parser monad now has Applicative/Alternative instances Currently, I am looking for people to give it a go reporting any bugs in the library or documentation, troubles building it, or changes/features they would like. I'm also interested in performance information. Most old Parsec code should be relatively easy but not trivial to port. There is a darcs repository on code.haskell.org. If nothing comes up, I'll put a package on Hackage in about a week or so. To get the code: darcs get http://code.haskell.org/ To build it, the standard cabal commands should work: http://haskell.org/haskellwiki/Cabal/How_to_install_a_Cabal_package Alternatively, you can use the cabal-install application: http://hackage.haskell.org/trac/hackage/wiki/CabalInstall The documentation can be generated also via the normal cabal routine, or via cabal-install.

1 0

reading from the cdrom drive on Red Hat
by Galchin Vasili 02 Feb '08

02 Feb '08

Hello, I wrote a simple program to read the contents of a cdrom: module Main where import Text.Printf import System.IO import System.Posix.Types import System.Posix.IO main = do fd <- openFd "/dev/cdrom" ReadOnly Nothing defaultFileFlags readCdRom fd 4096 closeFd fd readCdRom fd byteCount = do (buf, actualByteCount) = fdRead fd bytecount readCdRom fd byteCount When it executed it read thousands of 4096 blocks as I expected. It then got a "hardware error" which I suspect was the "end of the CD", i.e. the begininng of the "unlasered" part of the CD. Is there a better and more graceful way to detect and handle "end of data"? Thanks, ,Vasili

3 4

Simple network client
by Timo B. Hübel 01 Feb '08

01 Feb '08

Hello, I am using the very simple interactTCP example from [1] to play around with Haskell network programming but I just can't get a simple client for that example to work (it works like a charm with my telnet client, as described in the article). This is what I am trying to do with the client: main = withSocketsDo $ do hdl <- connectTo "localhost" (PortNumber 1234) hSetBuffering hdl NoBuffering hPutStr hdl "test message" res <- hGetContents hdl putStrLn (show res) The server looks like this: interactTCP :: Int -> (String -> IO String) -> IO () interactTCP port f = withSocketsDo $ do servSock <- listenOn $ PortNumber (fromIntegral port) waitLoop f servSock waitLoop f servSock = do bracket (fmap (\(h,_,_)->h) $ accept servSock) hClose (\h -> do hSetBuffering h NoBuffering hGetContents h >>= f >>= hPutStr h) waitLoop f servSock main = interactTCP 1234 (return . map toUpper) But is seems as some deadlocking occurs. Both programs just hang around doing nothing. By inserting some debug output I was able to make sure that the client successfully connects, but the data interchange just does not start. Because the whole thing works using telnet, I suspect that I am doing something fundamentally wrong in the client ... Any hints are greatly appreciated. Thanks, Timo [1] http://stephan.walter.name/blog/computers/programming/haskell/interacttcp.h…

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anybody can tell me the pronuncation of "haskell"?
by slofslb＠sina.com 01 Feb '08

01 Feb '08

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20 39

hxt memory useage
by Matthew Pocock 01 Feb '08

01 Feb '08

Hi, I've been using hxt to process xml files. Now that my files are getting a bit bigger (30m) I'm finding that hxt uses inordinate amounts of memory. I have 8g on my box, and it's running out. As far as I can tell, this memory is getting used up while parsing the text, rather than in any down-stream processing by xpickle. Is this a known issue? Matthew

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Announce: CC-delcont 0.2
by Dan Doel 01 Feb '08

01 Feb '08

Hello all, After much distraction and laziness on my part (my apologies), I have finally gotten around to putting together a new release of the delimited continuations library CC-delcont. It is now available on hackage. Relevant changes include: * Now builds in GHC-6.8.x * Builds with -Wall (and the code was cleaned up to make as little noise as possible) (Thanks to gwern for the above) Also included is a new module, Control.Monad.CC.Cursor, which provides some functions for reifying traversals into cursors that can be passed around and manipulated. It's still in its infancy, but I hope to eventually include generalized zippers and such. GHC 6.8 or greater is required to build, and haddock 2.0 or greater is required to generate the documentation. Links: * hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/CC-delcont-0.2 * darcs: http://code.haskell.org/~dolio/CC-delcont/ * a brief tutorial: http://haskell.org/haskellwiki/Library/CC-delcont (I've not had too much feedback on this, so if anyone has trouble following some sections, or has ideas on how to better explain delimited continuations, changes are welcome.) Once again, if you discover any bugs, or have any suggestions, don't hesitate to let me know. -- Dan Doel

1 0

derive Pretty?
by Greg Fitzgerald 01 Feb '08

01 Feb '08

Is it possible to automatically derive instances of Pretty<http://haskell.org/ghc/docs/latest/html/libraries/haskell-src/Language-Hask…>? If no, what do most do when it comes to pretty-printing large data types? Thanks, Greg

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Fwd: Re: [Haskell-cafe] Re: Implementing fixed-sized vectors (using datatype algebra?)
by Wolfgang Jeltsch 01 Feb '08

01 Feb '08

Hello Ryan, I hope, it’s okay to forward your message to the list: > Date: Freitag, 1. Februar 2008 01:41 > From: "Ryan Ingram" <ryani.spam(a)gmail.com> > To: "Wolfgang Jeltsch" <g9ks157k(a)acme.softbase.org> This representation is not exactly the same when you include _|_. For example: > data None -- only _|_ / undefined are members of this type. > data Pair a b = Pair a b > > -- There are three distinct inhabitants of the type Pair None (Pair None > None): v1, v2, v3 :: Pair None (Pair None None) > v1 = undefined > v2 = Pair undefined undefined > v3 = Pair undefined (Pair undefined undefined) > > -- whereas there are only two inhabitants of (None, None, None): > p1, p2 :: (None, None, None) > p1 = undefined > p2 = (undefined, undefined, undefined) You could solve it this way: > data PairL a b = PairL a !b where (a,b,c) is syntactic sugar for PairL a (PairL b (PairL c ())) Now we are back to only having two inhabitants of the type: > x1, x2 :: PairL None (PairL None (PairL None ())) > x1 = undefined > x2 = PairL undefined (PairL undefined (PairL undefined ())) There are still potential efficiency issues, although this could be worked out in the compiler; right now it's a single operation to get from a tuple to any member, but in PairL it takes n operations to get from the root to the nth elment of the tuple. The "unbox-strict-fields" optimization can fix this. On 1/31/08, Wolfgang Jeltsch <g9ks157k(a)acme.softbase.org> wrote: > Well, the representation (D1,D2,D9) might be considered more readable. It > has the disadvantage of a fixed maximum size for the numbers. Which takes > me to a point I had already considered some time ago: Wouldn't it be good > if we had just a type > > data Pair val1 val2 = Pair val1 val2 > > and if then (val1,val2,…,valn) would just be syntactic sugar for this: > > val1 `Pair` (val2 `Pair` (…(valn `Pair` ())…))

2 1

Relevance and applicability of category theory
by aaltman＠pdx.edu 01 Feb '08

01 Feb '08

Category theory seems to have an inconsistent relationship to Haskell - both documentation and the language's implementations of categorical concepts. I come from a math background that makes the Haskell's tight coupling to its mathematical foundation very appealing. But, I may have found some inconsistencies. Whether you agree or not I hope we can get some discussion going that will clarify the wikibooks, etc. My issues: 1. Are Haskell monads useful in a truly categorical sense? 2. Is Haskell's functor class misnamed? 3. Haskell arrows and Haskell monads have a misleading relationship 1. Categorical monads are a class of functors, that is, morphisms on Cat. Haskell's monads are at least a bit closer to the categorical idea than Haskell's functors by virtue of having the same domain and codomain: Hask -> Hask. I think applicability of Haskell monads beyond sequencing computation, and the validity of their definition, would be much more clear if someone explained the meaning of adjoint functors to and from Hask. In other words, provide the mathematical characterization to make Haskell monads a precise representation of categorical monads on Hask. 2. Functors are structure preserving maps in the category Cat. The Haskell Functor class represents structure preserving maps in the category Hask, which seem to me more like the categorical notion of arrows or the algebraic notion of homomorphisms. If we talk about functors relating to Haskell, it seems more likely we'd be referring to functors to or from the category Hask than functions (or arrows or whatever) between elements of Hask. Maybe categorical functors are useful as an abstract characterization of programs themselves: a program defines a functor from the problem domain into Hask, or from Hask into output in a problem domain. The name "Arrow" is already taken; what about renaming Functor to Automorphism? 3. I believe the documentation stating that Haskell arrows are a generalization of Haskell monads, but arrows are a categorical thing too and in that context bear a much more distant relationship to monads. Does a Haskell arrow have Hask as domain and codomain? Or is one particular element in Hask its domain and possibly another its codomain? Those are not at all the same thing. My guess is that the concept of Hask is too murky to be any use right now. The documentation may be more clear by avoiding it until we work out a formal definition... or is there one already? - Aaron Altman

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announcing darcs 2.0.0pre3
by David Roundy 01 Feb '08

01 Feb '08

We are happy to announce the third prerelease version of darcs 2! Darcs 2 features numerous improvements, and it seems that we have fixed most of the regressions, so we're looking for help, from users willing to try this release out. Read below, to see how you can benefit from this new release, and how you can help us to make the final darcs 2 release the best ever! The third prerelease features (apart from numerous bug and performance regression fixes) a completely rewritten rollback command and new progress-reporting functionality. If darcs takes more than a couple of seconds for a given operation and provides you with no feedback as to what it's up to, let us know, so we can fine-tune the progress-reporting output! I would especially like to thank Mark Stosberg for his tireless work triaging old bugs in our bug tracker and writing tests to be added to our test suite for those still present! For more details, and instructions on obtaining darcs 2.0.0pre3, see: http://wiki.darcs.net/index.html/DarcsTwo David

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RE: [Haskell] Announce: Yi 0.3
by Bayley, Alistair 01 Feb '08

01 Feb '08

> From: haskell-bounces(a)haskell.org > [mailto:haskell-bounces@haskell.org] On Behalf Of > Jean-Philippe Bernardy > > * homepage: http://haskell.org/haskellwiki/Yi Took a quick look around and saw this: * GTK frontend works in Win32 So Yi works on Windows? hs-plugins was broken for Windows for a while, so I'm wondering if this has been fixed too. Does Yi use hs-plugins, or does it go straight down to ghc? (looking at the yi.cabal file seems to indicate no dependency on hs-plugins) Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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Re: [Haskell-cafe] RE: [Haskell] Announce: Yi 0.3
by Peter Verswyvelen 01 Feb '08

01 Feb '08

Is YI also an IDE for creating Haskell code? I guess it's not, it's "just" a text editor right? I mean, if it talks to GHC directly, it could neatly take over some tricks used in Visual Haskell (on the fly type inference, good completion, etc), only much much easier (without the COM layer, directly in Haskell).

1 0

Re: [Haskell-cafe] Simple network client
by Gary Bickford 31 Jan '08

31 Jan '08

Wasn't there a Linux file system (possibly a FUSE user-space one) that worked on writable CDs? IIRC it worked by marking the previous copy of the file as erased, and writing a new copy. On Wed, 2008-01-30 at 23:05 -0500, haskell-cafe-request(a)haskell.org wrote: > > PS: I would love to see an immutable filesystem that does not allow > writing to files, it only creates new files and garbage collects files > that have no incoming reference anymore... Just like a garbage > collected heap, and a bit like an OLAP databases (as far as I remember > my DB theory...) Besides the performance bottleneck, does something > like that exists? > > Plan 9's venti is somewhat similar to this. though it's really a > storage backend that you implement a filesystem on top of, and the fs > winds up having a write cache, which is mutable in practice. The > interesting thing is that the block's location is the cryptographic > hash of its contents, which leads to all sorts of neat properties (as > well as requiring immutability). > -- "Isn't it funny how the Global Village includes everybody but the villagers?" (http://wiki.laptop.org/go/OLPC_Publications)

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Re: [Haskell-cafe] Mission: To take args from an n-tuple ... generally
by Martin Hofmann 31 Jan '08

31 Jan '08

> > I wondered, why not take an n-tuple of arguments s.t. > > > > multApply' :: (a1->a2->...->an->o) -> (a1,(a2,(...(an,o)...))) -> > o > > > I'm not sure what you're trying to do here. Why is there an o in the > argument? Also, do you really mean the number of arguments expected to > match the number of arguments given? > You are right. It should rather be multApply' :: (a1->a2->...->an->o) -> (a1,(a2,(...(an-1,an)...))) -> o as e.g. in: multApply' take (2,['a','b','c']) > Also you might want to check out Olegon polyvariadic functions: > http://okmij.org/ftp/Haskell/vararg-fn.lhs Thanks, I will have a look at this. Martin

1 0

CFP - PLMMS 2008
by Jacques Carette 31 Jan '08

31 Jan '08

FIRST CALL FOR PAPERS Second Workshop on Programming Languages for Mechanized Mathematics (PLMMS 2008) http://events.cs.bham.ac.uk/cicm08/workshops/plmms/ As part of CICM / Calculemus 2008 Birmingham, UK, 28-29 July 2008 This workshop is focused on the intersection of programming languages (PL) and mechanized mathematics systems (MMS). The latter category subsumes present-day computer algebra systems (CAS), interactive proof assistants (PA), and automated theorem provers (ATP), all heading towards fully integrated mechanized mathematical assistants that are expected to emerge eventually (cf. the objective of Calculemus). The two subjects of PL and MMS meet in the following topics, which are of particular interest to this workshop: * Dedicated input languages for MMS: covers all aspects of languages intended for the user to deploy or extend the system, both algorithmic and declarative ones. Typical examples are tactic definition languages such as Ltac in Coq, mathematical proof languages as in Mizar or Isar, or specialized programming languages built into CA systems. Of particular interest are the semantics of those languages, especially when current ones are untyped. * Mathematical modeling languages used for programming: covers the relation of logical descriptions vs. algorithmic content. For instance the logic of ACL2 extends a version of Lisp, that of Coq is close to Haskell, and some portions of HOL are similar to ML and Haskell, while Maple tries to do both simultaneously. Such mathematical languages offer rich specification capabilities, which are rarely available in regular programming languages. How can programming benefit from mathematical concepts, without limiting mathematics to the computational worldview? * Programming languages with mathematical specifications: covers advanced "mathematical" concepts in programming languages that improve the expressive power of functional specifications, type systems, module systems etc. Programming languages with dependent types are of particular interest here, as is intentionality vs extensionality. * Language elements for program verification: covers specific means built into a language to facilitate correctness proofs using MMS. For example, logical annotations within programs may be turned into verification conditions to be solved in a proof assistant eventually. How need MMS and PL to be improved to make this work conveniently and in a mathematically appealing way? These issues have a very colorful history. Many PL innovations first appeared in either CA or proof systems first, before migrating into more mainstream programming languages. Some examples include type inference, dependent types, generics, term-rewriting, first-class types, first-class expressions, first-class modules, code extraction etc. However, such innovations were never aggressively pursued by builders of MMS, but often reconstructed by programming language researchers. This workshop is an opportunity to present the latest innovations in MMS design that may be relevant to future programming languages, or conversely novel PL principles that improve upon implementation and deployment of MMS. We also want to critically examine what has worked, and what has not. Why are all the languages of mainstream CA systems untyped? Why are the (strongly typed) proof assistants so much harder to use than a typical CAS? What forms of polymorphism exist in mathematics? What forms of dependent types may be used in mathematical modeling? How can MMS regain the upper hand on issues of "genericity" and "modularity"? What are the biggest barriers to using a more mainstream language as a host language for a CAS or PA/ATP? Submission ---------- Submission works through EasyChair http://www.easychair.org/conferences/?conf=plmms2008 Two kinds of papers will be considered: * Full research papers may be up to 12 pages long. Authors of accepted papers are expected to present their work on the workshop in a regular talk. * Position papers may be up to 4 pages long. The workshop presentation of accepted position papers consists of two parts: a stimulating statement of certain issues or challenges by the author, followed by a discussion in the plenum. Papers should use the usual ENTCS style http://www.entcs.org/prelim.html (11 point version), and will be reviewed by the program committee. Informal workshop proceedings will be circulated as a technical report. We also plan post-workshop proceedings of improved research papers, or position papers that have been completed into full papers, as a special issue in a journal; papers from both PLMMS 2007 and 2008 will be considered here (details to follow). Programme Committee ------------------- Jacques Carette (Co-Chair) (McMaster University, Canada) John Harrison (Intel Corporation, USA) Hugo Herbelin (INRIA, Ecole polytechnique, France) James McKinna (Radboud University Nijmegen, Netherlands) Ulf Norell (Chalmers University, Sweden) Bill Page Christophe Raffalli (Universite de Savoie, France) Josef Urban (Charles University, Czech Republic) Stephen Watt (ORCCA, University of Western Ontario, Canada) Makarius Wenzel (Co-Chair) (Technische Universitaet Muenchen, Germany) Freek Wiedijk (Radboud University Nijmegen, Netherlands) Important Dates --------------- * Submission deadline - 5 May 2008 * Notification of acceptance - 6 June 2008 * Final version - 7 July 2008 (approximately) * Workshop - 28-29 July 2008

1 0

Mission: To take args from an n-tuple ... generally
by Martin Hofmann 31 Jan '08

31 Jan '08

Dear Community. I have recently read Joel Koerwer's posting how to evaluate a function of type (a->a->...->a->a), taking the arguments from a list (http://haskell.org/pipermail/haskell-cafe/2006-October/018658.html) Therefore, he introduced a function multApply: multApply :: (a->a->...->a->a) -> [a] -> a I wondered, why not take an n-tuple of arguments s.t. multApply' :: (a1->a2->...->an->o) -> (a1,(a2,(...(an,o)...))) -> o I naively tried to modify Joel's code, but in vain. As far as I can deduce from the error messages, GHC fails to fix the accordant types. However, in my understanding the type solely depends on the type of the passed function. Or am I wrong? Maybe there is a reason nobody has tried it this way? Following the code. First Joel's original multApply and then my attempt to define multApply'. ------------------------ MultApply.hs ------------------------------ {-# OPTIONS -fglasgow-exts -fallow-overlapping-instances #-} module MultApply where class MultApply func arg | func -> arg where multApply :: func -> [arg] -> arg instance MultApply (a->a) a where multApply f (x:xs) = f x multApply f _ = error "MultApply: one too few args" instance MultApply cascade a => MultApply (a -> cascade) a where multApply f (x:xs) = multApply (f x) xs multApply f _ = error "MultApply: n too few args" -- some random examples oneArg = multApply sqrt [25..] twoArg = multApply (+) [1..] fiveArg = multApply (\a b c d e -> sqrt ((a+b)^2+(d-e)^2)-5*c) [13..] class MultApply' f arg out | f -> arg out where multApply' :: f -> arg -> out instance MultApply' (a->b) a b where multApply' f x = f x multApply' f _ = error "MultApply: one too few args" instance MultApply' cascade a2 b => MultApply' (a1 -> cascade) (a1,a2) b where multApply' f (x,xs) = multApply' (f x) xs multApply' f _ = error "MultApply: n too few args" -------------------End File ------------------------ Hope I didn't stumble in a stupid newbie question. Thanks a lot to everybody who could give me some explanation and hints. Cheers, Martin

2 1