- Haskell-Cafe - Haskell.org

ghc binaries for sunos, hpux, aix, irix, and osf1?
by Goetz Isenmann 23 Aug '04

23 Aug '04

Hi! Are there other binary ghc versions available besides those on http://www.haskell.org/ghc/download.html, that I can use for ghc bootstrap on sunos (5.5.1-5.9), hpux (10.20 and 11.x), aix (4.3-5.2), irix (6.5), and osf1 (4.0-5.1)? -- Goetz Isenmann

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Fun with multi-parameter type classes
by Sam Mason 22 Aug '04

22 Aug '04

Hi, I've been getting into Haskell over the past few months and have just come up against a bit of a brick wall when trying to encapsulate some of the data structures in my code nicely. Basically what I want to have, is a type class where one of the intermediate values is opaque with respect to code using its implementations. This is a simplified version of what I'm trying to accomplish: class Foo t where encode :: String -> t decode :: t -> String instance Foo Int where encode = read decode = show test = decode . encode This currently fails, because the type checker insists on trying to figure out what its type should be - even though it shouldn't be needed. Any suggestions on how to encode this sort of thing? And if it is possible, can it be extended to multiple type parameters? as this is really what I want to use it for. About the only way I can think of "fixing" it, is by turning the code inside out - sort of like the way an AST drives the compiler, but without knowing how it represents things internally. Thanks, Sam

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hugs, ghc portability
by Vadim Zaliva 20 Aug '04

20 Aug '04

Hi! I have following code: import Data.Bits xcomp :: Int -> Int -> Int xcomp a m = (xor a (complement m)) which compiles fine under GHC. However hugs does not like it, since they intentionally did not do: --instance Bits Int How can I resolve this to have this code work under GHC and hugs? Sincerely, Vadim -- "La perfection est atteinte non quand il ne reste rien a ajouter, mais quand il ne reste rien a enlever." (Antoine de Saint-Exupery)

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Logic programming in Haskell
by Stefan Monnier 20 Aug '04

20 Aug '04

Has anyone already tried to embed prolog-style logic programming as a Haskell library? Kind of like Schelog but for Haskell? I know about Curry, but I'd like a Haskell library rather than another language. Stefan

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Re: [Haskell-cafe] Fun with multi-parameter type classes
by Jon Cast 19 Aug '04

19 Aug '04

> Hi, > > I've been getting into Haskell over the past few months and have just > come up against a bit of a brick wall when trying to encapsulate > some of the data structures in my code nicely. Basically what I > want to have, is a type class where one of the intermediate values > is opaque with respect to code using its implementations. This is > a simplified version of what I'm trying to accomplish: > > class Foo t where > encode :: String -> t > decode :: t -> String > > instance Foo Int where > encode = read > decode = show > > test = decode . encode > > This currently fails, because the type checker insists on trying to > figure out what its type should be - even though it shouldn't be > needed. The intermediate type /is/ needed---it's a (hidden) parameter to your `encode' and `decode' functions. Why do you think it shouldn't be? <snip> Jon Cast

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Re: [Haskell-cafe] Logic programming in Haskell
by Benderjgdefault＠aol.com 19 Aug '04

19 Aug '04

In a message dated 8/19/04 11:11:00 AM, monnier(a)iro.umontreal.ca writes: >Has anyone already tried to embed prolog-style logic programming as >a Haskell library? Kind of like Schelog but for Haskell? > >I know about Curry, but I'd like a Haskell library rather than >another language. No doubt you are looking for an implementation, not papers, but I would like to point a selection of papers dealing with embedding logic programming in Haskell (on my Haskell bibliography site): http://haskell.readscheme.org/appl.html#logic This includes both the Seres and Spivey papers, but also a couple of papers by Ralf Hinze. Also, since you mention Schelog, perhaps you would also find interesting KANREN, a more recent logic-programming-in-Scheme system by Dan Friedman, Oleg and others: http://kanren.sourceforge.net Jim

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Haskell extension/improvement
by Ron de Bruijn 18 Aug '04

18 Aug '04

I was playing with QuickCheck and I just wanted to put all of my tests in a list, but that's not possible, because of the fact that a list can only contain values of the same type. So concrete I would like to write down this: prop_RevRev xs = reverse (reverse xs) == xs where types = xs::[Int] --trivial test prop_Simple = True == True whatIwant::(Testable a)=>[a] whatIwant = [prop_RevRev, prop_Simple] testAll::IO () testAll = do sequence_ $ map quickCheck whatIwant quickCheck can work on all Testable values, so why can't a list (any datastructure) can't hold Testable values? What this gives you is, a lot more flexibility. Just like you can define your functions on interfaces, now you can use interfaces in your datastructures. I can't think of any reason why it couldn't be implemented in any Haskell compiler. I saw this page: http://www.haskell.org/hawiki/ExistentialTypes but you still have to explicitly add the relation via Obj (and that's bad). Regards, Ron P.S. If it already exist in this exact way, how is it called? _______________________________ Do you Yahoo!? Express yourself with Y! Messenger! Free. Download now. http://messenger.yahoo.com

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puzzle: prove this floorSqrt correct
by blaetterrascheln＠web.de 17 Aug '04

17 Aug '04

-- Here's the discrete version of Newton's method for finding -- the square root. Does it always work? Any literature? floorSqrt :: Integer -> Integer floorSqrt n | n>=1 = detect (iterate (\x->(x+n`quot`x)`quot`2) 1) where detect (x:xs@(y:z:_)) | x==z = min x y | otherwise = detect xs isFloorSqrt n x = x*x <= n && n < (x+1)*(x+1) main = print$ all (\n->isFloorSqrt n (floorSqrt n)) [1..1000000] ________________________________________________________________ Verschicken Sie romantische, coole und witzige Bilder per SMS! Jetzt neu bei WEB.DE FreeMail: http://freemail.web.de/?mc=021193

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Haskell extension/improvement
by MR K P SCHUPKE 16 Aug '04

16 Aug '04

See http://www.cwi.nl/~ralf/HList for a paper which shows how to implement a heterogeneous list in haskell, and how to implement operations on it (amongst other things)... Keean.

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automatic Haskell indentations
by Henning Thielemann 16 Aug '04

16 Aug '04

Looking for automatic indentation of Haskell code I found the thread http://www.haskell.org/pipermail/haskell-cafe/2003-August/005000.html It ended up with many suggestions for manual formatting of code. I wonder if there is some tool which simply formats a Haskell program. A tool like 'indent' (or 'm3pp' for Modula-3) which processes data from stdin to stdout could be nicely integrated into NEdit.

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