December 2004 - Haskell-Cafe

Quzzle
by Thomas Davie 04 Dec '04

04 Dec '04

Hi, Having read an interesting, but simplistic article on the development of Quzzle in Haskell on slashdot (http://developers.slashdot.org/article.pl?sid=04/12/04/ 0116231&threshold=1&tid=159&tid=156). I was wondering if anyone knew of any more in depth reviews of what Jim Lewis did to create the puzzle. Is there a paper available on it? Thanks Tom Davie -- Computer Science is as much about computers as astronomy is about telescopes -- Edsgar Dijkstra

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Re: [Haskell-cafe] Non-technical Haskell question
by Keean Schupke 04 Dec '04

04 Dec '04

Some of the features they are adding to c# are pretty cool. Nothing you can't do in Haskell, but it does have the advantage of familiar syntax. On the other hand they say it is easier to teach functional programming to people who have never programmed before. I was of course thinking of how to persuade someone to adopt Haskell as yet another programming language. Marc Charpentier wrote: > On 3 déc. 2004, at 17:18, Keean Schupke wrote: > > Its not yet another programming language - it's the future and you > don't want to be left behind... > > Keean. > > > But Erik Meijer wrote (http://blogs.gotdotnet.com/emeijer/) > > " Pure functional programmers, your days are numbered. The grim reaper > is knocking at your door." > > :-/ > > > > > Marc Charpentier

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Classes in type declarations in Hugs
by John Goerzen 03 Dec '04

03 Dec '04

Hello, I have this line: type CPResult a = MonadError CPError m => m a GHC (with various command-line options I'm already using) compiles this fine. hugs, with -98 +o, complains: Syntax error in input (unexpected `=>') How do I make this work both places?

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Top-level state debate on the wiki
by George Russell 03 Dec '04

03 Dec '04

Ben Rudiak wrote (snipped): > I put up a wiki page summarizing the main proposals for top-level > mutable state. The type-dictionary approach isn't there yet, but there's > a space for it; I'll probably fill it in within the next 24 hours unless > someone else feels like doing it first. > > Please add more detail, objections, examples. Especially examples! > > Here's the page: > > http://haskell.org/hawiki/GlobalMutableState I have added a summary of the type-dictionary approach. I recommend other people look at this page and, if there is something they disagree with, amend it so that their own view is reflected. IMO the WiKi approach is an excellent way of obtaining consensus and providing an overview of the topic.

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problem building hmake on Mac OS X
by Steven Elkins 02 Dec '04

02 Dec '04

Hello everyone, I'm trying to build hmake on version 10.3.6 of Mac OS, having installed the ghc 6.2.2 dmg I found on haskell.org, but I'm encountering the following problem: Steven-Elkins-Computer:~/haskell/hmake-3.09 sge$ make cd src/hmake; make HC=ghc all config /Users/sge/haskell/hmake-3.09/lib/powerpc-Darwin7/config:9: *** missing separator. Stop. make: *** [targets/powerpc-Darwin7/hmake-ghc] Error 2 Here's lib/powerpc-Darwin7/config: Steven-Elkins-Computer:~/haskell/hmake-3.09 sge$ cat lib/powerpc-Darwin7/config BUILDWITH=ghc BUILDOPTS="" INSTALLVER="3.09 (2004-11-13)" INSTALLINFO="config: powerpc-Darwin7/ by sge(a)Steven-Elkins-Computer.local on Thu Dec 2 04:43:46 EST 2004" BUILDBASEDIR=/Users/sge/haskell/hmake-3.09/targets READLINE="-DUSE_READLINE=1 -lreadline" EXE= GHCSYM=#pragma GCC set_debug_pwd "/Users/sge/haskell/hmake-3.09" 602 TRUE=/usr/bin/true In case Gmail wraps this, line 9 has the oracular '602'. Finally, here's the ./configure output: Steven-Elkins-Computer:~/haskell/hmake-3.09 sge$ ./configure --prefix=/usr/local Configuring for hmake... [ 3.09 (2004-11-13) ] -------- Looking for already-installed Haskell compilers: Looking for hbc... (not found) Note: LMLDIR/HBCDIR variables must be set to enable detection of hbc. Looking for ghc... found 6.2.2 Looking for nhc98... (not found) I am guessing that you want to use ghc to build hmake. Now I'm creating targets/powerpc-Darwin7/hmake3.config for your installation. Done. -------- Configuration report for hmake. (You can re-run configure to change settings before proceeding.) You wish (eventually) to install the following components in these locations: (Installation directories are not created/checked at this stage.) Final install root: /usr/local hmake binaries: /usr/local/lib/hmake/powerpc-Darwin7 Scripts: /usr/local/bin Man pages: /usr/local/man/man1 Now we check/create your build directories: Config directory: targets/powerpc-Darwin7 Build directory root: /Users/sge/haskell/hmake-3.09/targets (exists) Object files build in: /Users/sge/haskell/hmake-3.09/targets/powerpc-Darwin7 (exists) Executables and libs: /Users/sge/haskell/hmake-3.09/lib/powerpc-Darwin7 (created) I have guessed you will build hmake with: ghc Testing for the curses library: -lncurses (detected) Testing for the readline library: -lreadline (detected) Executables need .exe suffix? no (detected) Found /usr/bin/true not /bin/true Adding Makefile config script to /Users/sge/haskell/hmake-3.09/lib/powerpc-Darwin7... Adding build scripts for hmake, hmake-config, and hi to /Users/sge/haskell/hmake-3.09/script... Updating targets/powerpc-Darwin7/hmake3.config... Saving current configuration in targets/powerpc-Darwin7/config.cache Done. Steven-Elkins-Computer:~/haskell/hmake-3.09 sge$ Thanks, Steve

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RE: [Haskell-cafe] Re: Non-technical Haskell question
by Simon Peyton-Jones 02 Dec '04

02 Dec '04

| I also have a very small start on a "haskell for hackers" ("hackers" in | the non-evil sense) sort of document. One this doesn't ignore I/O as | "hard" or "unimportant". I/O in Haskell doesn't suck. It's just that a | lot of people in the community don't have it as a high priority, I | think. As a shameless plug, have you tried "Tackling the awkward squad?". Indeed I/O in Haskell doesn't suck. http://research.microsoft.com/%7Esimonpj/papers/marktoberdorf Simon

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Top-level state debate on the wiki
by Ben Rudiak-Gould 02 Dec '04

02 Dec '04

I put up a wiki page summarizing the main proposals for top-level mutable state. The type-dictionary approach isn't there yet, but there's a space for it; I'll probably fill it in within the next 24 hours unless someone else feels like doing it first. Please add more detail, objections, examples. Especially examples! Here's the page: http://haskell.org/hawiki/GlobalMutableState (It also includes an explanation of why I chose that title, though of course you're welcome to dispute that too.) -- Ben

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memory leak in Random.randoms or makeList?
by S. Alexander Jacobson 01 Dec '04

01 Dec '04

Using ghci, I am getting this error message: *Main> timeOp $ print $ sizeFM bigFM' GHC's heap exhausted: current limit is 268435456 bytes; >From this code: makeList x = map ((\x->x `mod` range).abs) $ Random.randoms (Random.mkStdGen x)::[Int] range=100000 fmRecords' n = listToFM $ take n $ zip (makeList 100) (makeList 200) fmRecords n = listToFM $ take n $ zip [range..] [range..] fmSize=10^6 bigFM = fmRecords fmSize bigFM' = fmRecords' fmSize bigFM works fine so the leak is obviously within makeList. I just don't understand how makeList could produce this error... -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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Forcing type conversion - probably FAQ(?)
by Dusan Kolar 01 Dec '04

01 Dec '04

Hello, I'm trying to make work the following code (I'm using GHCi with flags -fglasgow-exts -fallow-undecidable-instances): infixl 6 :+, :- infixl 6 .+, .- data TMyExpr = TMyExpr :+ TMyExpr | TMyExpr :- TMyExpr | Val Int | Id String class MkExpr a b where (.+) :: a -> b -> TMyExpr (.-) :: a -> b -> TMyExpr instance MkExpr Int Int where (.+) a b = (Val a) :+ (Val b) (.-) a b = (Val a) :- (Val b) instance MkExpr Int TMyExpr where (.+) a b = (Val a) :+ b (.-) a b = (Val a) :- b instance MkExpr TMyExpr Int where (.+) a b = a :+ (Val b) (.-) a b = a :- (Val b) instance MkExpr TMyExpr TMyExpr where (.+) a b = a :+ b (.-) a b = a :- b It compiles fine, no problem. Nevertheless, writing (3::Int) .+ (4::Int) seems to me quite clumsy, but 3 .+ 4 does not work. :-( It says the 3 is from class Num and no variant is present for it, I know, it is not present, but how to force it to convert it to Int "automatically"? When I try to incorporate instance (Num a, Num b) => MkExpr a b where (.+) a b = (Val . round a) :+ (Val . round b) (.-) a b = (Val . round a) :- (Val . round b) the situation is even worse. :-( I tried several modifications, but they don't work either. :-\ I was trying to find the discussion (I wonder whether it went on the similar topic through the list recently), but failed. :-( If someone can just point me to any resource I could study the possible solutions - maybe I put wrong data to google. ;-) Or just to stop me, if I'm trying to do impossible... :-\ Thx, Dusan

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Re: [Haskell-cafe] Re: ACIO versus Execution Contexts
by Adrian Hey 01 Dec '04

01 Dec '04

On Tuesday 30 Nov 2004 3:02 pm, Lennart Augustsson wrote: > I reiterate: not even device drivers written in C use TWIs. > (Well, at least not quality drivers. :)) A finite pool of N devices is still a unique resource. Ultimately you have to contain the problem locally with a modular solution, or all the unique state handle "buck passing" to higher levels (via who knows what intermediate modules) takes you all the way up to main. This is technically feasible, but highly un-modular and certainly not a desirable characteristic of any programming language (at least not one whose use I would advocate). Regards -- Adrian Hey

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