March 2009 - Haskell-Cafe

Re: [Haskell-cafe] Design Patterns by Gamma or equivalent
by Gregg Reynolds 18 Mar '09

18 Mar '09

2009/3/11 Mark Spezzano <mark.spezzano(a)chariot.net.au>: > I’m very familiar with the concept of Design Patterns for OOP in Java and > C++. They’re basically a way of fitting components of a program so that > objects/classes fit together nicely like Lego blocks and it’s useful because > it also provides a common “language” to talk about concepts, like Abstract > Factory, or an Observer to other programmers. In this way one programmer can > instantly get a feel what another programmer is talking about even though > the concepts are fundamentally abstract. > > Because Haskell is not OO, it is functional, I was wondering if there is > some kind of analogous “design pattern”/”template” type concept that > describe commonly used functions that can be “factored out” in a general > sense to provide the same kind of usefulness that Design Patterns do for > OOP. Basically I’m asking if there are any kinds of “common denominator” > function compositions that are used again and again to solve problems. If > so, what are they called? > You might find it useful to read the original works upon which the whole "design pattern" economy is based, namely Christopher Alexander's books (http://www.patternlanguage.com/leveltwo/booksframe.htm?/leveltwo/../booksto…) I liked "Notes on the Synthesis of Form", which predates his pattern language stuff. My $0.02: design patterns became popular in the imperative language community precisely because such languages lack the formal discipline of functional languages. Alexander came up with the notion of a pattern language in order to bring some kind of discipline and abstraction to observed regularities in architecture, urban design, etc. By definition such a language cannot have anything close to formal semantics, any more than a natural language lexicon can have formal semantics. Alexander's writing is very interesting and thought provoking, but I'm not sure it has much to offer the world of functional programming. Programmers used Alexander's ideas to try to bring some order to both specifications and programs. A pattern language is a natural for trying to describe a real-world problem one is trying to solve. Imperative programmers also used it to describe programming patterns. Implementations of things like Observer/VIsitor etc. are ad-hoc, informal constructions; the equivalent in a functional language is a mathematical structure (feel free to fix my terminology). I don't think one needs design patterns for Haskell; it has mathematics and more-or-less formal semantics. Who needs "Visitor" when you have "For All"? Although design patterns may still be useful for describing a real-world problems I suspect one would be better off dumping the notion of design pattern, the better to avoid cognitive dissonance when trying to think in purely functional terms. Cheers, -gregg

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How can I check which thunks are piling up on the stack?
by Gü?nther Schmidt 17 Mar '09

17 Mar '09

Hi, How can I check which thunks are piling up on the stack? Günther

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OpenGL and Cabal installation
by Mark Spezzano 17 Mar '09

17 Mar '09

Hi all, I’m trying desperately to get OpenGL up and running. I type >cabal.exe configure and get the following ... checking GL/glut.h usability... no checking GL/glut.h presence... no checking for GL/glut.h... no checking for GLUT library... no checking for GL/glut.h... (cached) no checking GLUT/glut.h usability... no checking GLUT/glut.h presence... no checking for GLUT/glut.h... no configure: error: no GLUT header found, so this package cannot be built See `config.log' for more details. Where is it looking for these glut.h files? I’ve tried putting them everywhere in my PATH but msys won’t find them. Cheers, Mark Spezzano No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.18/2008 - Release Date: 17/03/2009 4:25 PM

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a newbies confusion with repositories - darcs or git
by Gü?nther Schmidt 17 Mar '09

17 Mar '09

Hi, now that I'm finished with my haskell app I take the opportunity to follow up on some things I hadn't quite understood in my so far short venture into the haskell world. Means: Prepare for a number of naive posts to follow. I had the impression that darcs was the preferred repository for haskellers, but there also is git. So far I've just been using the goodol' svn. But since I have the ambition to become a real haskeller I was gonna make myself acquainted with darcs. Should I skip that and head straight for git? Günther

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Haskell and the Cell Processor
by Galchin, Vasili 17 Mar '09

17 Mar '09

Hello, http://www.power.org/resources/devcorner/cellcorner .... Is there project to port GHC to the Cell? Seems like a really cool challenge. Regards, Vasili

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Has anybody replicated =~ s/../../ or even something more basic for doing replacements with pcre haskell regexen?
by Thomas Hartman 17 Mar '09

17 Mar '09

Is there something like subRegex... something like =~ s/.../.../ in perl... for haskell pcre Regexen? I mean, subRegex from Text.Regex of course: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex-compat Thanks for any advice, thomas.

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can GHC build an executable from a C source file?
by Manlio Perillo 17 Mar '09

17 Mar '09

Hi. I'm checking if it possible to build an executable from C source files only. As an example: #include <stdio.h> int main () { printf("hello world\n"); return 0; } $ghc --make foo.c However this only produces the object file, foo.o; it does not build the executable file. What is the reason for this behaviour? I have tested with GHC 6.8.2. Thanks Manlio

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Data.Binary
by Galchin, Vasili 17 Mar '09

17 Mar '09

Hello, I installed ghci on my work Windows machine. If I do a ":m +Data.Word", everything is OK. If I a ":m +Data.Binary", can't be found. Why? Regards, Vasili

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RE: SQL Parsers in Haskell
by Larry Coleman 17 Mar '09

17 Mar '09

> Hi Haskelleers > > Has anybody written a SQL parser in Haskell (and is willing to share the > code) ? > > Greetings, > > Mads Lindstrøm I have a mostly-working SQL parser that I wrote to help with DBA tasks at work. I'm under one of the standard employment IP agreements, however, so my employer owns the code. I have asked about having it released, but that process will take some time. I'll post to the group if/when it ever happens. Larry Coleman

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Apologies for spamming Planet Haskell
by Bjorn Buckwalter 17 Mar '09

17 Mar '09

Dear Planet Haskell readers, Just want to apologize for spamming Planet Haskell. I did some minor formatting edits of old posts and it seems Planet Haskell picked them up and republished them. I didn't expect this to happen (Google Reader doesn't do that) and will be more careful about gratuitously editing old posts in the future. Thanks, Bjorn Buckwalter

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