- Haskell-Cafe - Haskell.org

Harder than you'd think
by Andrew Coppin 13 Jun '10

13 Jun '10

So the other day I was writing some code, and I ended up wanting to have a collection of data indexed in more than one way. In other words, I wanted fast lookup with several different keys. Initially I built something using two Data.Map objects to represent the two lookup keys, but then I needed up needing more keys per value than that, so I decided I should write a small library to abstract the whole thing. What I ended up writing is this: http://www.hpaste.org/fastcgi/hpaste.fcgi/view?id=25782 It sorta kinda works, but man, take a look at the first line. That's *a lot* of type-system abuse to make it go. And it strikes me that if you had two keys, both of which happen to have the same type (e.g., String)... what then? On the other hand, it's not like you can go lookup :: KeyID -> Key -> Container -> Maybe Value since the type of both the container and the key depend on which key you want to access. Man, this is way, way harder than I realised! Does anybody have a less-insane way of doing this?

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Re: [Haskell-cafe] Harder than you'd think
by Andrew Coppin 13 Jun '10

13 Jun '10

Philippa Cowderoy wrote: > On 13/06/2010 14:52, Andrew Coppin wrote: >> Marc Weber wrote: >>>> Does anybody have a less-insane way of doing this? >>> >>> Sure: >>> type MyMap = Map (KeyID, Key) Value >>> >>> Don't use multiple keys. Put the keys into a tuple and use that as key. >>> >>> Let me know whether this is what you were looking for. >> >> Trouble is, this requires you to have *all* the keys to perform a >> single lookup. You can't do a lookup on just one attribute. >> > > No it doesn't - think sum/or, not product/and, your tuple's (KeyID, > Key) not (Key1, Key2, Key3...). > Oh, I see - so you enter (1, author), (2, date), (3, time), etc? That then requires all keys to have the same type - although I think for my needs I can put together an ADT to fix that...

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Fwd: [Haskell-cafe] Literate programming
by aditya siram 13 Jun '10

13 Jun '10

I understand that this becomes less of an issue when > you become more experienced with haskell. Still it will always be a good > way > to promote haskel-style solutions. > I dunno, John uses noweb to good effect. Things like import statements along with the function definition are pretty nice and not achievable with Literate Haskell. > > I don't have any problems with LaTeX, but a less verbose solution would do > just fine. > You don't really need to know a lot of LaTex to use noweb. I'm no LaTex expert and I found the source easy to read. > My biggest problem is actually literate programming in conjunction with > leksah. Can anybody comment on this issue? Do you guys use leskah at all? > Unfortunately literate programming doesn't really have the tool support yet. I use emacs for Haskell development and loading Haskell code in to the REPL will be an issue if you're editing a noweb file. Currently this is the only thing keeping me from starting a large (> 2000 LOC) literate project -deech > > -- > Martin > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Literate programming
by Martin Drautzburg 13 Jun '10

13 Jun '10

Hello all, Is literate programming something you guys actually do (I only know that Paul Hudak does), or is it basically a nice idea from days gone by? In case you do, then how do you do it? Do you use lhs2TeX or what? Do you use "bird" style of full-blown LaTeX? Does any of you use leksah? I failed to see any support for literate programming in leksah. It candies the backslashes in e.g. \documentclass{article} to λdocumentclass{article}. In case you don't, then how do you document your code? If you write a paper which explains what your code does, then how do you do that? -- Martin

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Fwd: [Haskell-cafe] Proposal to solve Haskell's MPTC dilemma
by Carlos Camarao 13 Jun '10

13 Jun '10

I forgot to cc the message below to haskell-cafe... ---------- Forwarded message ---------- From: Carlos Camarao <carlos.camarao(a)gmail.com> Date: Thu, Jun 10, 2010 at 4:40 PM Subject: Re: [Haskell-cafe] Proposal to solve Haskell's MPTC dilemma To: "Brandon S. Allbery KF8NH" <allbery(a)ece.cmu.edu> On Wed, Jun 9, 2010 at 1:51 AM, Brandon S. Allbery KF8NH < allbery(a)ece.cmu.edu> wrote: > On Jun 8, 2010, at 15:32 , Job Vranish wrote: > > It seems like this would make working with MPTCs much easier. > When programming, I generally want to only specify the minimum amount of > information to make my code logically unambiguous. > If the code contains enough information to infer the proper instantiation > without the use of an FD, then I shouldn't need to add a FD. > It seems like this would have much more of a "it just works" feel than the > currently alternatives. > > > I can't help but think that the "it just works" mentality leads to duck > typing. > > -- > brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery(a)kf8nh.com > system administrator [openafs,heimdal,too many hats] allbery(a)ece.cmu.edu > electrical and computer engineering, carnegie mellon university KF8NH > > Perhaps I am missing something, but if we have, say, quack o::IO() (or in_the_forest o:: IO(), or, say, f o:: Bool ( en.wikipedia.org/wiki/Duck_typing)) then: "o" can be a duck, or a dragon, that quacks, but there is no dynamic binding: o's type must be the only type with a function quack in this context (it cannot be both duck and dragon in this context, one being chosen dynamically according to the value of "o"). This avoids the problem of calling quack for an incorrect value (there can be no dragons into a pond, trying to impersonate a duck). Cheers, Carlos

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Re: [Gtk2hs-users] Woes on MacOS 10.6 - linking issues -now working, but Glade is missing in v0.11 and v0.10.1 still won't compile SOLVED compile of 10.1
by Brett Giles 12 Jun '10

12 Jun '10

Finally figured it out - leave the scripts for ghc and hsc2hs alone and do the configure for gtk2hs 0.10.11 like this: ./configure --with-hsc2hs='--cc-flag=-m32 --ld-flag=-m32' On Jun 12,2010, at 3:53 PM, Brett Giles wrote: > Hi everyone, > > Thanks for the variety of suggestions - I resolved this by uninstalling the Haskell-platform DMG based package and using the one from macports. I then, as mentioned elsewhere, manually modified my hsc2hs shell script to ensure the correct code was generated. > > However, I see that the cabal install for version 11 contains no Glade modules. I saw there was a patch posted by Andy Stewart for it a while back, is there any ETA for it for the public? > > I am, (so sad for me:) a bit hooped as I was going to give a demo of a program in a couple of days, but my code depends heavily on Glade and I can't seem to get the prior version of Gtk2HS (0.10.1) to compile at all. (Issues with x86_64 vs i386 - but I have tried for three hours to get the magic combination of modifications to the ghc script, the hsc2hs script and environment variable to no avail). > > If anyone has had luck on getting the 10.1 version to build (on a brand new install of OSx v10.6.3, macports Haskell Platform meaning GHC is 6.10.4, I'd love to hear how you did it. > > (I did check out the variety of tickets related to this, especially http://hackage.haskell.org/trac/ghc/ticket/3400 and the recent conversations on this list between Chris K. and Axel. > > > On Jun 11,2010, at 2:40 AM, Axel Simon wrote: > >> Hi Brett, >> >> On 11.06.2010, at 04:53, Brett Giles wrote: >> >>> Hi Folks >>> >>> I seem to have Gtk2HS 0.11 installed, but not quite working. Interestingly, I can run a demo, such as the hello/World.hs example, directly in ghci. However, when I try to do a ghc --make on any code containing gtk2hs I get a link error like this: >>> >>> Undefined symbols: >>> "_iconv_close", referenced from: >>> _hs_iconv_close in libHSbase-4.2.0.0.a(iconv.o) >>> (maybe you meant: _hs_iconv_close) >>> "_iconv", referenced from: >>> _hs_iconv in libHSbase-4.2.0.0.a(iconv.o) >>> (maybe you meant: _hs_iconv_open, _hs_iconv , _hs_iconv_close ) >>> "_iconv_open", referenced from: >>> _hs_iconv_open in libHSbase-4.2.0.0.a(iconv.o) >>> (maybe you meant: _hs_iconv_open) >>> ld: symbol(s) not found >>> >>> >>> I do have libiconv installed as a universal library via macports. gtk, glade etc., are also universal installed via macports. >>> >> >>> I downloaded the OSX Haskell Platform package and am running ghc 6.12.1 >>> >> >> >> The iconv issue is usually that you also have a libiconv that Apple ships. The platform ghc probably links against that while macports (and thus Gtk+) uses its own. I have no idea who's to blame here but I guess you should be trying to change your LD_LIBRARY_PATH or your DYLD_LIBRARY_PATH to /opt/sw since that contains the more complete version. >> >> Cheers, >> Axel > > Brett Giles > Grad Student, Formal Methods, Category Theory, > University of Calgary > brett.giles(a)ucalgary.ca > > > > > ------------------------------------------------------------------------------ > ThinkGeek and WIRED's GeekDad team up for the Ultimate > GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the > lucky parental unit. See the prize list and enter to win: > http://p.sf.net/sfu/thinkgeek-promo > _______________________________________________ > Gtk2hs-users mailing list > Gtk2hs-users(a)lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/gtk2hs-users > > Brett Giles Grad Student, Formal Methods, Category Theory, University of Calgary brett.giles(a)ucalgary.ca

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Re: [Haskell] ANNOUNCE: Sifflet visual programming language, release 0.1.7
by Henning Thielemann 12 Jun '10

12 Jun '10

On Fri, 11 Jun 2010, Ben Millwood wrote: > On Fri, Jun 11, 2010 at 2:52 PM, Henning Thielemann > <lemming(a)henning-thielemann.de> wrote: >> >> I'm uncertain whether fgl conforms to the package versioning policy, but >> if it does, then changes in its Cabal file should not bother sifflet. >> Thus upper bound fgl < 5.4.3 should be restrictive enough. >> > > The PVP says that one of the first two numbers are required to change > if an API change is likely to break code using it, so < 5.5 would > probably suffice. A bump to fgl-5.4.3 might include API *extensions* that may break sifflet, if it imports entire FGL modules in an unqualified way.

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Similarities between web programming and functional programming
by Nilanjan Raychaudhuri 12 Jun '10

12 Jun '10

Hi all, As a newbie into functional programming and especially Haskell I am curious to know how functional programming style fits into building web applications? And how it compares to building web apps in Ruby or Java. Any pointer to article/literature will be helpful. Thanks Nilanjan

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Re: [Gtk2hs-users] Woes on MacOS 10.6 - linking issues -now working, but Glade is missing in v0.11 and v0.10.1 still won't compile
by Brett Giles 12 Jun '10

12 Jun '10

Hi everyone, Thanks for the variety of suggestions - I resolved this by uninstalling the Haskell-platform DMG based package and using the one from macports. I then, as mentioned elsewhere, manually modified my hsc2hs shell script to ensure the correct code was generated. However, I see that the cabal install for version 11 contains no Glade modules. I saw there was a patch posted by Andy Stewart for it a while back, is there any ETA for it for the public? I am, (so sad for me:) a bit hooped as I was going to give a demo of a program in a couple of days, but my code depends heavily on Glade and I can't seem to get the prior version of Gtk2HS (0.10.1) to compile at all. (Issues with x86_64 vs i386 - but I have tried for three hours to get the magic combination of modifications to the ghc script, the hsc2hs script and environment variable to no avail). If anyone has had luck on getting the 10.1 version to build (on a brand new install of OSx v10.6.3, macports Haskell Platform meaning GHC is 6.10.4, I'd love to hear how you did it. (I did check out the variety of tickets related to this, especially http://hackage.haskell.org/trac/ghc/ticket/3400 and the recent conversations on this list between Chris K. and Axel. > > > On Jun 11,2010, at 2:40 AM, Axel Simon wrote: > >> Hi Brett, >> >> On 11.06.2010, at 04:53, Brett Giles wrote: >> >>> Hi Folks >>> >>> I seem to have Gtk2HS 0.11 installed, but not quite working. Interestingly, I can run a demo, such as the hello/World.hs example, directly in ghci. However, when I try to do a ghc --make on any code containing gtk2hs I get a link error like this: >>> >>> Undefined symbols: >>> "_iconv_close", referenced from: >>> _hs_iconv_close in libHSbase-4.2.0.0.a(iconv.o) >>> (maybe you meant: _hs_iconv_close) >>> "_iconv", referenced from: >>> _hs_iconv in libHSbase-4.2.0.0.a(iconv.o) >>> (maybe you meant: _hs_iconv_open, _hs_iconv , _hs_iconv_close ) >>> "_iconv_open", referenced from: >>> _hs_iconv_open in libHSbase-4.2.0.0.a(iconv.o) >>> (maybe you meant: _hs_iconv_open) >>> ld: symbol(s) not found >>> >>> >>> I do have libiconv installed as a universal library via macports. gtk, glade etc., are also universal installed via macports. >>> >> >>> I downloaded the OSX Haskell Platform package and am running ghc 6.12.1 >>> >> >> >> The iconv issue is usually that you also have a libiconv that Apple ships. The platform ghc probably links against that while macports (and thus Gtk+) uses its own. I have no idea who's to blame here but I guess you should be trying to change your LD_LIBRARY_PATH or your DYLD_LIBRARY_PATH to /opt/sw since that contains the more complete version. >> >> Cheers, >> Axel Brett Giles Grad Student, Formal Methods, Category Theory, University of Calgary brett.giles(a)ucalgary.ca

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Looking for Haskell presenter in/around Columbus area
by Nilanjan Raychaudhuri 12 Jun '10

12 Jun '10

Hi all, I run a small meet up group called "Columbus polyglot programmer meet up group" ( http://www.meetup.com/The-Columbus-Polyglot-Programmers-Meetup-Group/) where bunch of us get together once in a month and talk about various programming languages. There is quite a bit of interest in Haskell and functional programming in general among the group. I was wondering whether anyone from the list who lives around Columbus, ohio area would be interested to talk about Haskell. Thanks Nilanjan

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