February 2005 - Haskell

Evaluating expressions given as String
by Javier García-Vivó Albors 08 Feb '05

08 Feb '05

Hello everybody. I'm working on a haskell project in which I need to evaluate haskell expressions that are given in an input File. For instance: A file containing "Peter==Peter" or "3+2==5" or "home in [a-z]*sex[a-z]*" (see I need to use regular expressions too) is given as input The file contents are read as String type and I need to evaluate them to True or False. I'm looking for the way to parse and translate these expressions in order to evaluate them. Thanks for you help. J. ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.

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help with some basic code that doesn't work
by pablo daniel rey 08 Feb '05

08 Feb '05

hello i'm new to haskell so i'm sorry if this is a stupid question, but i'm having problems with some basic code. the code : data Maybe Dir = Just Dir | Nothing data Dir = Left | Right | Up | Down data Piece = Vertical | Horizontal | CodeA | CodeB flow = [(Horizontal, Left, Left), (Horizontal, Right, Right), (Vertical, Down, Down), (Vertical, Up, Up), ................ etc ] fst :: (a,b,c) -> a fst (x,y,z) = x scnd :: (a,b,c) -> b scnd (x,y,z) = y third :: (a,b,c) -> c third (x,y,z) = z element :: [(Piece, Dir, Dir)] -> Maybe Dir element [] = Nothing element xs = Just (third (head xs)) chgDir :: Piece -> Dir -> Maybe Dir chgDir p d = element (filter (\x -> p == (fst x)) (filter (\x -> d == (scnd x)) flow)) the error i get : Instances of (Eq Dir, Eq Piece) required for definition of chgDir i don't know what's happening. help!!! thanks in advance

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ANNOUNCE: new FGL version (Feb 2005)
by Martin Erwig 07 Feb '05

07 Feb '05

FGL - A Functional Graph Library, Version: February 2005 ======================================================== I am happy to announce a new release of the Functional Graph Library for Haskell, a collection of graph algorithms and tools. Changes since the last release (from January 2004): * fixed an import error in Basic.hs * removed Eq instance of gr because it caused overlapping instance problems. Instead the function equal defined in Graph.hs can be used * added some more functions to the export list of DFS.hs * changed the definition of LPath into a newtype to avoid overlapping instances with lists * fixed the Makefile (for GHC and GHCi) Download: http://eecs.oregonstate.edu/~erwig/fgl/haskell/ Please email comments, bug reports, etc. to erwig(a)cs.orst.edu -- Martin

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Re: xemacs & haskell major mode
by Surendra Singhi 07 Feb '05

07 Feb '05

Jon Fairbairn wrote: > On 2005-01-24 at 16:32MST Surendra Singhi wrote: > >>Is there any ilisp or slime like package for haskell, which integrates >>haskell with xemacs or emacs and provides a kind of integrated >>development environment? >>I am using Hugs 98. > > > Does <URL: > http://www.haskell.org/pipermail/haskell/2004-November/015015.html > >>help? > > I downloaded the haskell mode from that site and I was trying to configure it, but during the process I ran into this error Debugger entered--Lisp error: (void-function charsetp) signal(void-function (charsetp)) byte-code("..." [buf data kill-buffer signal] 3) find-file-noselect("c:/Documents and Settings/Owner/My Documents/haskell practice/picture.hs") experimental-dragdrop-drop-url-default(#<misc-user-event (dragdrop-drop-dispatch (dragdrop-URL "file:c:/Documents and Settings/Owner/My Documents/haskell practice/picture.hs"))> (dragdrop-URL "file:c:/Documents and Settings/Owner/My Documents/haskell practice/picture.hs")) apply(experimental-dragdrop-drop-url-default (#<misc-user-event (dragdrop-drop-dispatch (dragdrop-URL "file:c:/Documents and Settings/Owner/My Documents/haskell practice/picture.hs"))> (dragdrop-URL "file:c:/Documents and Settings/Owner/My Documents/haskell practice/picture.hs"))) dragdrop-drop-do-functions(((experimental-dragdrop-drop-url-default t t) (experimental-dragdrop-drop-mime-default t t)) #<misc-user-event (dragdrop-drop-dispatch (dragdrop-URL "file:c:/Documents and Settings/Owner/My Documents/haskell practice/picture.hs"))> (dragdrop-URL "file:c:/Documents and Settings/Owner/My Documents/haskell practice/picture.hs")) byte-code("..." [object experimental-dragdrop-drop-functions event event-over-text-area-p dragdrop-extents-done (byte-code "Æ!Ç!È!É‰¬…ÊËÉ\"ˆ ¬‚ Ì!ˆÍ Î Ï#‰Éa¬”ÐÑ\nÏ\"#ˆÎ Ï\n$‰ªh-É‡" [window cpos ext buffer event pos event-window event-point event-closest-point nil throw dragdrop-extents-done select-window window-buffer extent-at experimental-dragdrop-drop-functions dragdrop-drop-do-functions extent-property object] 6) dragdrop-drop-do-functions] 4) dragdrop-drop-find-functions(#<misc-user-event (dragdrop-drop-dispatch (dragdrop-URL "file:c:/Documents and Settings/Owner/My Documents/haskell practice/picture.hs"))> (dragdrop-URL "file:c:/Documents and Settings/Owner/My Documents/haskell practice/picture.hs")) dragdrop-drop-dispatch((dragdrop-URL "file:c:/Documents and Settings/Owner/My Documents/haskell practice/picture.hs")) The code in my .init file is (setq load-path (cons "C:\\Program Files\\XEmacs\\xemacs-packages\\lisp\\haskell-mode\\" load-path)) (setq auto-mode-alist (append auto-mode-alist '(("\\.[hg]s$" . haskell-mode) ("\\.hi$" . haskell-mode) ("\\.l[hg]s$" . literate-haskell-mode)))) (autoload 'haskell-mode "haskell-mode" "Major mode for editing Haskell scripts." t) (autoload 'literate-haskell-mode "haskell-mode" "Major mode for editing literate Haskell scripts." t) (add-hook 'haskell-mode-hook 'turn-on-haskell-decl-scan) (add-hook 'haskell-mode-hook 'turn-on-haskell-doc-mode) (add-hook 'haskell-mode-hook 'turn-on-haskell-indent) Am I doing anything wrong? I am using Xemacs 21.4.13 Thanks. -- Surendra Singhi www.public.asu.edu/~sksinghi/

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[newbye] 'Just a'
by Yuri D'Elia 06 Feb '05

06 Feb '05

Hi all. I'm experimenting with haskell and its type system. I've done a function which scans a list, and returns "Just a" value if the element is found, or Nothing. get :: a -> Maybe a and implemented getAorB :: Maybe a -> Maybe a -> a getAorB a b = ... a function which returns "Just (get a)" or "Just (get b)" if (get a) is Nothing (excluding failures in both). By now, I've implemented it in terms of pattern matching: getAorB a b = f (get a) (get b) where f (Just a) Nothing = a f Nothing (Just a) = a but I'd like to know if there are other possible ways to do it, possibly without enforcing an evaluation order like pattern matching does.

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Re: [Possible Spam]RE: [Haskell] Job Posting (Looking for a few good functionalprogrammers)
by Yaron Minsky 04 Feb '05

04 Feb '05

David Bergman wrote: >Yaron, > >This is probably out-of-topic, but: are you, or have you considered, using >the .NET implementation of OCaml. I managed - painstakingly - to integrate >it into a toy .NET project of mine, using .NET Direct3D, and see some virtue >in that combination. > > I've been following OCaml/.NET integration, and it does seem potentially quite interesting, particularly in a business environment like ours where all of the traders use Windows machines. Which .NET implementation did you look at, OCamIL? Or F#? >If only we Haskellers would be as lucky: both a fast implementation and an >integrated one with a Real (trademark...) environment such as .NET :-( > >/David > > > >>-----Original Message----- >>From: haskell-bounces(a)haskell.org >>[mailto:haskell-bounces@haskell.org] On Behalf Of Yaron Minsky >>Sent: Thursday, February 03, 2005 3:28 PM >>To: S. Alexander Jacobson >>Cc: haskell(a)haskell.org >>Subject: Re: [Haskell] Job Posting (Looking for a few good >>functionalprogrammers) >> >>S. Alexander Jacobson wrote: >> >> >> >>>Yaron, would you mind sharing the reason your firm chose OCaml over >>>Haskell for your applications? >>> >>> >>I started the quantitative research group, and I knew OCaml >>very well, and didn't know Haskell except by reputation. As >>to the merits, it is my general impression that OCaml is >>faster, and is all around a more pragmatic language than >>Haskell. That's merely an ill-informed impression, but there it is. >> >>Yaron >> >> >> >>>For others, I would love to organize an informal gathering of NYC >>>Haskell programmers if there are any. If you are >>> >>> >>interested, please >> >> >>>contact me and I'll try to make it happen. >>> >>>-Alex- >>>______________________________________________________________ >>>S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com >>> >>> >>>On Thu, 3 Feb 2005, Yaron Minsky wrote: >>> >>> >>> >>>>Jane Street Capital (an affiliate of Henry Capital >>>><http://henrycapital.com>) is a proprietary trading >>>> >>>> >>company located >> >> >>>>in Manhattan. The quantitative research department is >>>> >>>> >>responsible for >> >> >>>>analyzing, improving, and generating trading strategies. It's an >>>>open and informal environment (you can wear shorts and a >>>> >>>> >>t-shirt to >> >> >>>>the office), and the work is technically challenging, including >>>>systems work, machine learning, statistical analysis, parallel >>>>processing, and anything that crosses our path that looks useful. >>>> >>>>One unusual attraction of the job is that the large >>>> >>>> >>majority of our >> >> >>>>programming is done in OCaml. Pay is competitive, and we're a >>>>reasonably small company (around 85 employees), so advancement is >>>>pretty quick for someone who performs well. >>>> >>>>Here's what we're looking for: >>>> >>>>- Top-notch mathematical and analytic skills. We want people who >>>>can solve difficult technical problems, and think clearly and >>>>mathematically about all sorts of problems. >>>> >>>>- Strong programming skills. Pretty much all of our >>>> >>>> >>programming is >> >> >>>>in OCaml, so being a solid caml hacker is a big plus. But we're >>>>also interested in great programmers who we are convinced will be >>>>able to pick up OCaml quickly, so anyone with a high-level of >>>>proficiency with functional languages could be a good match. >>>> >>>>- Strong Unix/Linux skills --- We're looking for someone >>>> >>>> >>who knows >> >> >>>>their way around the standard unix tools, can write >>>> >>>> >>makefiles, shell >> >> >>>>scripts, etc. We use a beowulf cluster for >>>> >>>> >>compute-intensive jobs, >> >> >>>>so experience programming for and administering clusters is a big >>>>plus. >>>> >>>>If you're interested (or have any students you think might >>>> >>>> >>be a good >> >> >>>>match) and would be willing to relocate to New York, please send a >>>>cover-letter and resume to: >>>> >>>>yminsky(a)janestcapital.com >>>> >>>> >>>>_______________________________________________ >>>>Haskell mailing list >>>>Haskell(a)haskell.org >>>>http://www.haskell.org/mailman/listinfo/haskell >>>> >>>> >>>> >>> >>> >>> >>_______________________________________________ >>Haskell mailing list >>Haskell(a)haskell.org >>http://www.haskell.org/mailman/listinfo/haskell >> >> >> > > > > >

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International M.Sc. Program in COMPUTATIONAL LOGIC
by Int. Center for Computational Logic 04 Feb '05

04 Feb '05

International M.Sc. Program in COMPUTATIONAL LOGIC The International Center for Computational Logic at the Technische Universitaet Dresden is offering a two-year study program, in English, leading to a master of science (M.Sc.) in computer science. This is part of the European Master's Program in Computational Logic, a distributed study program funded by the EU within Erasmus Mundus jointly run by the Free University of Bozen-Bolzano, the Technische Universitaet Dresden, the Universidade Nova de Lisboa, the Universidad Politecnica de Madrid and the Technische Universitaet Wien. Courses focus on logic and constraint programming, artificial intelligence, knowledge representation and reasoning, type theory, model theory, proof theory, equational reasoning, databases, natural language processing, planning and formal methods, among others. At the end of the programme a research master thesis has to be prepared. Prerequisites are a good knowledge of the basics of logic, and familiarity with mathematical reasoning. Knowledge of foundations of artificial intelligence and declarative programming is desirable. It is indispensable being fluent in English; German is not necessary at all, but there are facilities for studying it if desired. A bachelor in Computer Science, or equivalent degree, is required by the beginning of courses, in October 2005. Dresden, on the river Elbe, is one of the most important art cities of Germany. The economy is growing rapidly and Dresden is a top high-tech centre. AMD built the most modern chip factory in Europe, Infineon Technologies, Siemens and many other companies invest here. The possibilities of getting a job after the master are excellent. The University is very well equipped and the teachers/students ratio is close to 1. International contacts make it easy for interested students to continue pursuing a career in research. Deadline for applications is June 15, 2005, but applications are processed as they come. To apply, please send all the relevant documents by post to the address below. Further information is on the web at www.computational-logic.org including information about possible scholarships. Paper information material is available on request. Please give this message broad distribution. Sylvia Epp, secretary International Center for Computational Logic Technische Universitaet Dresden, D-01062 Dresden, Germany Tel: [49] (351) 463-38341 Fax: [49] (351) 463-38342 email: cl-secretary(a)Inf.TU-Dresden.DE

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RE: Implicit parameters:
by Simon Peyton-Jones 04 Feb '05

04 Feb '05

| Sent: 19 January 2005 14:42 | Unbound implicit parameter (?global_counter::IORef a) | arising from use of `get_unique' at Test.hs:17:13-22 | | Is this a bug? Is there some reason why this is not possible? (and if it | is not possible | shouldn't the documentation be changed to reflect this)... Keean's program has made me realise (yet again) that implicit parameters are a bit different to class constraints. Consider module Main where main = let ?x = 5 in print foo foo = woggle 3 woggle :: (?x :: Int) => Int -> Int woggle y = ?x + y GHC's current rules say that 'foo' is monomorphic, so we get foo :: Int but we also get an unbound top-level constraint (?x::Int). GHC emits a message like: Unbound implicit parameter (?x::Int) arising from use of `woggle' at ... The point is that THERE IS NO WAY FOR THIS CONSTRAINT TO GET BOUND, because we don't have a top-level binding form for implicit parameters. So it's stupid for 'foo' to be monomorphic. The situation is a bit different for class constraints: module Main where main = print fooC fooC = woggleC 3 woggleC :: Num a => a -> a wogglec y = y+1 'fooC' is monomorphic, so we get foo :: a, with a top-level constraint (Num a); and the defaulting mechanism fixes a=Integer, so all is well. Even in the absence of monomorphism, we might get some other use of 'fooC' in the module which fixes fooC's type. So it's *not* stupid for foo to be monomorphic. Possible conclusions A) Emit an error message at the definition of foo, saying that it needs a type signature. B) Change the rule so that we always generalise over the implicit parameters of *top-level* definitions, even in definitions that fall under the MR. C) Change the rule so that we always generalise over implicit parameters, whether top-level or nested. I'll do (A) for now, I think, since it improves the error message. For those that care, there are quite extensive notes about generalisation and implicit parameters in GHC's source code, here: http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/typecheck /TcSimplify.lhs?rev=1.144 (search for "Notes on implicit parameters"). Interestingly, the notes argue for (C), but that's not what is currently implemented in GHC, for reasons I don't remember. Perhaps compatibility with other implementations. Simon | -----Original Message----- | From: glasgow-haskell-users-bounces(a)haskell.org [mailto:glasgow-haskell-users- | bounces(a)haskell.org] On Behalf Of Keean Schupke | Sent: 19 January 2005 14:42 | To: glasgow-haskell-users(a)haskell.org | Subject: Implicit parameters: | | Question regarding implicit parameters... The GHC manual says: | | "Dynamic binding constraints behave just like other type class | constraints in that they are automatically propagated." | | But the following code produces an error: | | ------------------------------------------------------------------------ --------------------------------- | | main = do | var <- newIORef (0::Int) | let ?global_counter = var in f | | | f = do | a <- get_unique | putStr (showInt a "\n") | b <- get_unique | putStr (showInt b "\n") | c <- get_unique | putStr (showInt c "\n") | | | get_unique :: (?global_counter :: IORef Int) => IO Int | get_unique = readIORef ?global_counter | | ------------------------------------------------------------------------ ---------------------------------- | | If "(?global_counter :: IORef Int)" were a class constraint the type | signature | for 'f' could be derived automatically... but we get: | | Unbound implicit parameter (?global_counter::IORef a) | arising from use of `get_unique' at Test.hs:17:13-22 | | Is this a bug? Is there some reason why this is not possible? (and if it | is not possible | shouldn't the documentation be changed to reflect this)... | | Keean. | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users(a)haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users

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ANN: MissingPy First Release
by John Goerzen 04 Feb '05

04 Feb '05

Announcing MissingPy 0.1.0 http://quux.org/devel/missingpy ------------------------- What is MissingPy? ------------------------- It's two things: 1. A Haskell binding for many C and Python libraries for tasks such as data compression, databases, etc. This can be found in the MissingPy module tree. 2. A low-level Haskell binding to the Python interpreter to enable development of hybrid applications that use both environments. This can be found in the Python module tree. The Haskell bindings above use this environment. MissingPy permits you to call Python code from Haskell. It does NOT permit you to call Haskell code from Python. ------------------------- Major Features ------------------------- * GZip and BZip2 compression and decompression using the generic Handle-like HVIO interface * *dbm persistent storage using the generic AnyDBM interface * Low-level interface to Python for extending your own Haskell code * Many unit tests to verify proper functionality ** THIS IS CURRENTLY BETA-QUALITY CODE; MAJOR API FLUCTUATIONS MAY YET OCCUR. Future releases will likely feature HVFS virtual filesystem interfaces to ZIP and tar files, integration of Python's PCREs into Pesco's regexp system, a Haskell binding to PyOpenSSL, and other similar items. -- John Goerzen Author, Foundations of Python Network Programming http://www.amazon.com/exec/obidos/tg/detail/-/1590593715

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ANN: MissingH 0.9.0
by John Goerzen 03 Feb '05

03 Feb '05

Announcing MissingH 0.9.0 This release is being made now because it introduces several features that are important for my work on MissingPy (announcement forthcoming). New feature summary: * Perl-like regular expression operators (MissingH.Regex.Pesco) This module builds atop the standard POSIX Text.Regex module, extending it to be far more convenient with easier maching, grouping, and substitution operations. (Integrated from Pesco) * strToAL, strFomAL (MissingH.List) Converts any [(String, String)] and many other association lists to a simple string representation that can be stored on-disk or sent across the network. Also, re-generates the original list upon parsing the string representation. Used internally by MissingH.AnyDBM.StringDBM. * Persistent or non-persistent DBM storage class MissingH.AnyDBM is an abstraction for various mapping systems. MissingH itself provides an implementation using a non-persistent HashTable or FiniteMap, as well as a persistent StringDBM. Bindings to dbm, gdbm, dbhash, etc. are in the works and will be simple members of this typeclass. * Major cleaning up of the build system. Description of MissingH from README: ------------------------- What is MissingH? ------------------------- It's a collection of Haskell-related utilities. It is an extension of my earlier work developing MissingLib for OCaml. You can download MissingH from http://quux.org/devel/missingh. There is a mirror, with a few days' lag, at http://ftp.debian.org/debian/pool/main/m/missingh. ------------------------- Major Features ------------------------- * Powerful Logging Framework for Haskell This framework provides a system of hierarchical loggers and modular handlers permitting fine-grained logging with a great deal of control and yet a simple and fast interface. It's based on log4j for Java and logging for Python. Also included is a native-Haskell Syslog client. * Versatile modules to simplify everyday tasks: + FTP client library + E-mail client library + MIME types library to determine MIME types from files or URLs + Configuration file parser/generator * IO utilities make it easier to work with line-based text files and binary files * IO object virtualization so you can use one set of code to work on files of many different types * Filesystem virtualization so you can access variuos items with the same ease as your system's filesystem * Network utilities to streamline connections * List utilities including association list tools, list splitting, truncation, and delimiter joining * String utilities including removal of leading or trailing whitespace, joining, splitting, and truncation * Other utilities for threads, parers, filenames, etc. * Printf utilities for formatting strings * GZip decompression * Hundreds of unit tests to verify proper functionality * DBM module abstraction # arch-tag: 0.9.0 announcement

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