October 2009 - Haskell-Cafe

What *is* a DSL?
by Günther Schmidt 28 Oct '09

28 Oct '09

Hi all, for people that have followed my posts on the DSL subject this question probably will seem strange, especially asking it now. I have read quite a lot lately on the subject, most of it written by the great old ones, (come on guys you know whom I mean :)). What I could gather from their papers was, that a DSL is basically something entirely abstract as such, ie. it allows you build and combine expressions in a language which is specific for your problem domain. Irregardless of further details on how to do that, and there are quite a few, the crux as such is that they are abstract of "meaning". The meaning depends how you *evaluate* the expression, which can be in more than merely one way, which is where, as far as I understand it, the true power lies. So, you might wonder, since I figured it out this far, why ask what a DSL is? Because out there I see quite a lot of stuff that is labeled as DSL, I mean for example packages on hackage, quite useuful ones too, where I don't see the split of assembling an expression tree from evaluating it, to me that seems more like combinator libraries. Thus: What is a DSL? Günther

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cabal haddock hpc, exposed modules?
by Greg Fitzgerald 28 Oct '09

28 Oct '09

I have a cabal package that defines a few dozen modules, and I'm hoping to generate documentation and code coverage for all modules without listing each module explicitly. currently my .cabal includes: library exposed-modules: Language.Idl.Data, Language.Idl.Merge, Language.Idl.Parser, ...lots more... my Setup.hs includes an explicit system call to hpc: exec "hpc" ["markup" , "--include=Language.Idl.Data" , "--include=Language.Idl.Merge" , "--include=Language.Idl.Parser" ...all the same files as above... ] Questions: 1) Is there a way to create haddock docs for /all/ modules, instead of just the ones listed by 'exposed-modules'? 2) Is there a way to query cabal for the list of modules? Or by chance has hpc recently been integrated with cabal? Thanks, Greg

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Re: uu-parsinglib pKeyword
by S. Doaitse Swierstra 28 Oct '09

28 Oct '09

pToken [] = pSucceed [] pToken (x:xs) = (:) <$> pSym x <*> pToken xs pKeyword_Float = pToken "Float" etc Doaitse PS: this function has been defined in the module Text.ParserCombinators.UU.Derived On 28 okt 2009, at 17:39, Ozgur wrote: > Hi everybody, > > I am using the uu-parsinglib to parse a structured language and map > the results to some proper data structures. Thanks to Prof Doaitse > Swierstra (and other authors if any), it is fun to write a parser > using this library. > > I've been sending private mails to Doaitse about my questions, who > kindly gives nice replies everytime. But this time I thought I can ask > my question to the community, and give everyone the chance to benefit > from the answers. > > [After the intro, here comes my real question] > > I am trying to capture the following pattern. > > pKeyword_Int = ( \ _ _ _ -> "int" ) <$> pSym 'i' <*> pSym 'n' <*> pSym > 't' > pKeyword_Float = ( \ _ _ _ _ _ -> "float" ) <$> pSym 'f' <*> pSym 'l' > <*> pSym 'o' <*> pSym 'a' <*> pSym 't' > > As you can see there is an obvious pattern if you try to capture a > "keyword". If there were a function called pKeyword taking a string as > an argument and producing the necessary parser, things would be > easier. > > What I mean is, > > pKeyword_Int = pKeyword "int" > pKeyword_Float = pKeyword "float" > > I tried to create this pKeyword function myself but I couldn't manage > to do it. > > I can feel that, one can simply add a "<* pReturn []" to the ends of > every parser and write a recursion with this base condition. > > Any suggestions? > > PS: Actually I'm a little bit uncomfortable since there may be such a > function in the library already :)

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Cabal says "no installed version of base"
by John Velman 28 Oct '09

28 Oct '09

I'm on OS X Leopard 10.5.8, using ghc 6.10.4 from Haskell Platform. I'm trying to get a static .a library, callable from C, that I can use in an OS X Cocoa program. I've tried a very simple case (the one in Haskell Wiki Tutorials,"calling haskell from C") I've managed to make a Mac Cocoa application by adding the ghc generated .o program, plus adding one by one the needed Haskell libraries for "symbol not found" to my Xcode project. There should be a better way. I've tried just about everything I could find on creating Haskell libraries, with no joy. My latest try is to use Cabal, following advice found both in "How to write a Haskell program" and the Cabal users guide. My output from cabal -v configure tells me, among others: --- Reading installed packages... /usr/bin/ghc-pkg dump --global /usr/bin/ghc-pkg dump --user Reading available packages... Resolving dependencies... There is no installed version of base --- But when I do ghc-pkg dump --global it appears base is listed. Apparently, "no installed version of base" short circuits the whole process. Any suggestions, pointers to reading, whatever will be appreciated.

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Fwd: [Haskell-cafe] Market Place for Haskell development teams?
by Alberto G. Corona 28 Oct '09

28 Oct '09

forwarded to the list: Curt, Rubi and Pyton came into existencie without their internet libraries, but they would´nt be popular without them. Although I conffess I don´t know the history in detail. Academics is not mainstream. 2009/9/29 Curt Sampson <cjs(a)starling-software.com> > On 2009-09-29 13:18 +0200 (Tue), Alberto G. Corona wrote: > > > Java is part of the Java platform, that brought OS independence and > > interoperability at the right time. .Download-execution on the client > > was also a reason for the initial success of Java in the Internet era. > > I was a die-hard Java hacker from 1999 until some undetermined time in > the early-to-mid-2000s. (I abandoned it more or less completely sometime > around late 2005, if I recall correctly.) > > This may be somewhat anecdotal evidence, but I disagree with both > of your statements here. > Of course, I´m not talking about real advantages of Java or any PL. I told about the reasons that people used at the time to introduce the language in the mainstream, either is desirable this for haskell or not. I think it is. Nobody consider the runtime download of Java code important nowadays. Not even the cross-platform features. but it was marketeed at his time as such. > > Rubi and Python came with libraries targeted to Rapid development of > > Internet applications. > > No, neither originally "came" with that. > Rubi and Pyton came into existencie without their internet libraries, but they would´nt be popular without them. Although I conffess I don´t know the history in detail. > > What is the vehicle that haskell can use to enter the mainstream?. > > That may be the wrong question. "Avoid success at all costs" still > rings true to me. A year or so ago I seemed like one of the few on > the haskell-libraries list voting in favour of fixing API problems in > libraries, rather than etching in stone those problems in the name of > backwards compatibility so that we could "become more popular." > > Said above. We have different goals. > Do you really want, in 2020, to look back at the 2010 revision of the > Haskell standard and think, "we entrenched things that for a decade > everybody agreed was dumb"? > I see no problem in haskell having both. experimental and fixed versions. Haskell 2020 for you and me and haskell 2010 for my commercial code. Both woukd ve maintained and enriched by far more people. > > I can tell you, even when you're a Java enthusiast, there's nothing > more depressing than looking at java.util.Date and thinking, "That > should have been immutable, but it's going to be mutable for the rest of > eternity. We will never fix that." > > But let's try this again: > > > What is the vehicle that haskell can use to enter the mainstream?. > > Become more stupid. > > Is that a better answer? I'm not just a geek; I do marketing too (this > is what happens when you start your own company), and if you asked me, > using the utmost of my technical knowledge and marketing skills, to make > Haskell popular, this is what I'd recommend. > > Become more stupid may mean "give exactly what the people want" that transaltes to be more stable, give libraries, platforms etc. That is not a extra effor. that will come naturally as more people use the language. some people is naturally more abstract. some are more practical. > (I suppose it's a sign of my professionalism that to do this would > nearly break my heart, but if you wanted me to tell you the best way to > do this, and I couldn't tell you to get lost, that's what I'd say.) > > > Many people will play with Haskell in the spare time, and many of them > > will be permitted to develop some non critical applications at work. > > But that is all. > > Hm. So I suppose that this options trading system I'm working on, which > is the sole way our business makes money and is entirely written in > Haskell, doesn't actually exist. > > Congratulations.!! > > I think that all the current niches are filled, but new niches are > coming. > > Haskell already has a good niche. In fact, a brilliant one. We have > a whole bunch of academics doing truly wonderful stuff (imagine the > world without monads!--thank you Philip Wadler (and Eugenio Moggi)) > that the rest of us (relatively) dumb idiots can use to make our lives > better. We've got several very good implementations of the language, > one of which is a truly shit-hot compiler[1]. And we can use that to do > commercial applications quite comfortably[2]. > > Right. ;) > My personal opinion is, yes, let's let Haskell stick to the niche where > it's great, but it changes so fast that it's scary to everybody else. To > echo Paul Graham, I'm extremely happy to see my competition use Java. > > [1] Like that's so important. Ruby's standard implementation to this day > is an interpreter that implements all the popular extensions and has a > reasonably decent FFI. In Haskell-land, we call that "Hugs." It's only > because we have GHC as well that we can look down on Hugs; in the Ruby > (and Python, and PHP) worlds, they're saying that interpreters are just > fine for all sorts of "enterprise applications." > > [2] (Warning: self-promotion): > http://www.starling-software.com/misc/icfp-2009-cjs.pdf > > > Financial applications are an example of higher level programming > > where tasks usually performed by humans are now automatized and there > > is no or few traditions about that. The need to think at a higher > > level without being worried by side effects and other details are > > specially needed in such kind of areas. That's where haskell could > > have its own niche. > > Actually, I think that Haskell has a niche there not because of that > sort of thing, but merely because it's better than Java at doing what > Java does well, but scary enough that only small groups of brave > people who are comfortable with risk would ever attempt to use it. The > financial sector happens to have a lot more of those than many others. > > same concept in more plain words. I guess. > cjs > -- > Curt Sampson <cjs(a)starling-software.com> +81 90 7737 2974 > Functional programming in all senses of the word: > http://www.starling-software.com >

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[Haskell-cafe] hopefully, a very quick question about ByteString lib
by Iain Barnett 27 Oct '09

27 Oct '09

[1 of 1] Compiling Main ( sha1.lhs, interpreted ) import qualified Data.ByteString as B main = B.getLine >>= B.putStrLn Ok, modules loaded: Main. *Main> :main *** Exception: no buffering And just to make sure it's not something to do with GHCi or anything like that main = getLine >>= putStrLn [1 of 1] Compiling Main ( sha1.lhs, interpreted ) Ok, modules loaded: Main. *Main> :main hello hello Why am I getting an error when using the ByteString library? Iain

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ANN: haskell-mode 2.5
by Svein Ove Aas 27 Oct '09

27 Oct '09

Fellow Haskellers, I'm happy to announce the release of haskell-mode 2.5. * By web: http://projects.haskell.org/haskellmode-emacs/ * By darcs: http://code.haskell.org/haskellmode-emacs/ Furthermore, there is a change of maintainer; if you have issues, you should now contact me instead of Stefan Monnier. haskell-mode 2.5 ============= I was uncertain whether to mark this a minor or major release. On the one hand, very little has changed in core functionality. On the other, a new minor mode for indentation has been added: haskell-indentation.el, written by Kristof Bastiaensen. It will be familiar to those of you who have been tracking the CVS repository; there are only minor bug-fixes relative to the last version to be uploaded there. For the rest of you: haskell-indentation.el is an intelligent indentation mode in the style of haskell-indent.el, with a few changes to improve usability. Specifically, instead of a tab cycle, backspace is now used to reduce the nesting level, while tab will increase it. The behaviour is otherwise substantially the same; only valid nestings will be considered. It can be turned on by adding (add-hook 'haskell-mode-hook 'turn-on-haskell-indentation) to your .emacs file, as described in the README. As usual, it is mutually exclusive with the two other indentation modes. Known bugs: * Occasionally, the haskell-indentation parser will get stuck on what it considers to be invalid haskell code, and refuse to accept your commands; this includes, mainly, haskell-newline-and-indent. To avoid annoyance, if you bind RET to haskell-newline-and-indent, you should bind M-RET to plain newline. -- Svein Ove Aas

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Is there a null statement that does nothing?
by michael rice 27 Oct '09

27 Oct '09

It looks like both the THEN and the ELSE in an IF expression must each have an expression. What's a graceful way to do nothing in either or both slots, kind of like the Fortran CONTINUE statement. --mr ================ [michael@localhost ~]$ ghci GHCi, version 6.10.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> if (1==1) then else <interactive>:1:15: parse error on input `else' Prelude> if (1==1) then True else <interactive>:1:24: parse error (possibly incorrect indentation) Prelude> if (1==1) then True else False True Prelude>

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ANN: WFLP2010 2nd CFP: LNCS + invited speaker + abstract due Nov 9
by Pablo Nogueira 27 Oct '09

27 Oct '09

******************************************************************** Second Call For Papers 19th International Workshop on Functional and (Constraint) Logic Programming Madrid, Spain, January 17, 2010 http://babel.ls.fi.upm.es/events/wflp2010/ ********* colocated with Principles of Programming Languages POPL 2010 http://www.cse.psu.edu/popl/10/ ******************************************************************** IMPORTANT DATES Abstract Submission: November 9, 2009 Full Paper Submission: November 15, 2009 Acceptance Notification: December 15, 2009 Preliminary Proceedings: January 5, 2010 Workshop: January 17, 2010 SCOPE The aim of the Workshop on Functional and (Constraint) Logic Programming is to bring together researchers interested in functional programming and (constraint) logic programming with special emphasis on the integration of both paradigms and of other declarative programming extensions. It promotes the cross-fertilizing exchange of ideas and experiences among researchers and students from the different communities interested in the foundations, applications, and combinations of high-level declarative programming languages and related areas. The previous WFLP editions are: WFLP 2009 (Brasilia, Brazil), WFLP 2008 (Siena, Italy), WFLP 2007 (Paris, France), WFLP 2006 (Madrid, Spain), WCFLP 2005 (Tallinn, Estonia), WFLP 2004 (Aachen, Germany), WFLP 2003 (Valencia, Spain), WFLP 2002 (Grado, Italy), WFLP 2001 (Kiel, Germany), WFLP 2000 (Benicassim, Spain), WFLP'99 (Grenoble, France), WFLP'98 (Bad Honnef, Germany), WFLP'97 (Schwarzenberg, Germany), WFLP'96 (Marburg, Germany), WFLP'95 (Schwarzenberg, Germany), WFLP'94 (Schwarzenberg, Germany), WFLP'93 (Rattenberg, Germany), and WFLP'92 (Karlsruhe, Germany). LOCATION WFLP 2010 will be held on January 17, 2010 in Madrid, Spain, colocated with the 37th ACM SIGACT-SIGPLAN Symposium on Principles of Programming Languages (POPL 2010). WFLP 2010 solicits papers in all areas of functional and (constraint) logic programming, including but not limited to: * Foundations: formal semantics, logic variables, binding and abstract syntax, rewriting and narrowing, unification, constraint solving, dynamics, type theory, meta-theory, effects, etc. * Language Design: security, services, modules, type systems, multi-paradigm languages, concurrency and distribution, objects, libraries, generic programming, interoperability, etc. * Implementation: abstract machines, parallelism, compile-time and run-time optimizations, foreign-language interfaces, memory management, multi-threading, exploiting parallel hardware, etc. * Transformation and Analysis: abstract interpretation, specialization, partial evaluation, program transformation, program calculation, program proof, meta-programming, generative programming, etc. * Software Development: algorithms, data structures, design patterns, components and composition, specification, proof assistants, verification and validation, model checking, debugging, testing, profiling, tracing, etc. * Paradigm Integration: integration of declarative programming with other paradigms or features such as imperative, object-oriented, aspect-oriented, concurrent, real-time programming, event-driven architectures, etc. * Applications: education, industry, commercial uses, domain-specific languages, visual/graphical user interfaces, embedded systems, WWW applications, XML processing, artificial intelligence, knowledge representation and machine learning, deductive databases, advanced programming environments and tools, etc. SUBMISSIONS and PROCEEDINGS Authors are invited to submit papers presenting original unpublished work. Papers must be at most 15 pages long. Exceptionally, authors may surpass the page limit by providing well-marked appendices intended as reviewing aids. Appendices will not appear in the final publication. Submission categories include regular research papers, system descriptions, and short papers describing on-going work (at most 8 pages). Submissions must be formatted in Lecture Notes in Computer Science (LNCS) style. This requirement needs not apply to appendices. Papers should be submitted in pdf format electronically via the web-based submission site http://www.easychair.org/conferences/?conf=wflp2010 Preliminary proceedings will be available at the workshop. Selected authors will be invited to submit a full version of their papers after the workshop. Contributions accepted for the post-workshop proceedings will be published in Springer's Lecture Notes in Computer Science series. INVITED SPEAKER Mariangiola Dezani (University of Torino, Italy) PROGRAM CHAIR Julio Marino (Universidad Politecnica de Madrid, Spain) PROGRAM COMMITTEE Maria Alpuente (Universidad Politecnica de Valencia, Spain) Sergio Antoy (Portland State University, USA) Bernd Brassel (CAU Kiel, Germany) Olaf Chitil (Univ. of Kent, UK) Rachid Echahed (CNRS-IMAG, France) Santiago Escobar (Universidad Politecnica de Valencia, Spain) Moreno Falaschi (Universita di Siena, Italy) Murdoch Gabbay (Heriot-Watt University, UK) Maria Garcia de la Banda (Monash University, Australia) Victor Gulias (Lambdastream SL, Spain) Michael Hanus (CAU Kiel, Germany) Herbert Kuchen (Univ. of Muenster, Germany) Francisco Lopez-Fraguas (Universidad Complutense de Madrid, Spain) James Lipton (Wesleyan University, USA) Mircea Marin (Univ. of Tsukuba, Japan) Juan Jose Moreno-Navarro (Ministry of Science & Innovation, Spain) Brigitte Pientka (McGill University, Canada)

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A 3 line program --> Reid, Don, Daniel
by Philippos Apolinarius 27 Oct '09

27 Oct '09

Thank you for your help. I am sure that you are right as to the cause of the problem. However, I do not know what I should do to solve it. The Haskell program is generated by LaTeX macros. It is useless to import System.IO.UTF8. I did it. The system keeps producing the same error. What I need is to configure GHC to accept input from any editor, or text generating tool (like TeX). I suppose it is not very difficult to do it, since all other languages have it. I mean, Haskell is the only language where I cannot type a common word like "façade" without running into trouble. I will send you a slightly more complete program, so you can analyse the problem. One has two programs in Tex, and an example. The first file is haskell.gen and it defines the macro \haskell{} % Store in file haskell.gen % Last change 2007-05-23 \newcount\evalFilecount \evalFilecount=0 {\gdef\haskellSetup{% \csname newwrite\endcsname\progPort \immediate\openout\progPort H\jobname.hs % \immediate\write\progPort{module H\jobname}% \immediate\write\progPort{where}% \newlinechar=`\^^M% \newlinechar=`\^^M% }% } \newcommand{\haskell}{\begingroup \ifx\progPort\UNDEFINED \haskellSetup\fi% \catcode`\^^M=12 \haskellGen } \newcommand{\haskellGen}[1]{% \immediate\write\progPort{#1}% \endgroup } %end of file haskell.gen The second file is hask.ell and it defines \eval{}. It is slightly more complex than the previous one. Still, it is very simple. % Store in file hask.ell % Last change 2007-05-23 \newcount\evalFilecount \evalFilecount=0 {\gdef\evalSetup{% \csname newwrite\endcsname\outPort % Port name \immediate\openout\outPort \jobname.hs % \newlinechar=`\^^M% \immediate\write\outPort{import H\jobname}% \newlinechar=`\^^M% \immediate\write\outPort{import IO}% \newlinechar=`\^^M% \immediate\write\outPort{main= do }% \newlinechar=`\^^M% }% } \newcommand{\eval}{\begingroup \ifx\outPort\UNDEFINED \evalSetup\fi \global\advance\evalFilecount by 1 \edef\evalAuxFile{\jobname-G-H-C\the\evalFilecount}% \immediate\write\outPort { outh <- openFile "\evalAuxFile.ghc" { WriteMode;} }% {\immediate\openin0=\evalAuxFile.ghc \ifeof0 \immediate\closein0 \else \input \evalAuxFile.ghc \fi}% \catcode`\^^M=12 \evalBody } \newcommand{\evalBody}[1]{% \immediate\write\outPort{#1}% \immediate\write\outPort{ hClose outh;}% \endgroup } %end of file hask.ell Below, there is an example of how to use the above macros. Store it in file tudin.tex. \documentclass[12pt]{article} \usepackage[latin1]{inputenc} \usepackage[brazil]{babel} \usepackage{makeidx} \usepackage{wrapfig} \usepackage{pictexwd} \title{Calling Haskell from \LaTeX} \author{Philippos Apolinarius} \date{} \begin{document} \maketitle \input haskell.gen \input hask.ell % load \eval \eval{ hPutStrLn outh "Hello, facade!" } \eval{ hPutStrLn outh (show (fat 6)) } \haskell{ fat n | n<1= 1 fat n= n*fat(n-1) } \end{document} In order to use these examples, do the following: 1 --- Apply latex to tudin.tex: C:\hastex> latex tudin.tex 2 --- You have generated file tudin.hs and Htudin.hs. Execute tudin.hs: C:\hastex> runghc tudin.hs This action will generate two files: tudin-G-H-C1.ghc, and tudin-G-H-C2.ghc. There is one file for each instance of \eval{}. 3 --- If you run latex tudin.tex again, it will load these two files, and insert the results of the Haskell programs into the resulting pdf or dvi files. C:\hastex> latex tudin.tex My friend has a lot of complex Clean libraries that she uses to generate postscript images of her designs. The trouble is that she needs to compile Clean souce code generated by the two LaTeX macros. SInce Clean needs two files per module (implementation module and definition module), the two LaTeX macros are quite complex. Clean looks a lot like Haskell. Therefore, I believe that she will not have any difficulty in translating the code to Haskell. It is true that input/output is different in Clean and Haskell. However, input/output can be centered in the main function. Unhappily she needs to write all those French, Swiss, Italian and Spanish names, like façade, Antoní Gaudi, Xenákes, etc. BTW, if you discover how to use strings in Haskell, one could write Haskell-café, instead of Haskell-cafe. __________________________________________________________________ Looking for the perfect gift? Give the gift of Flickr! http://www.flickr.com/gift/

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