July 2004 - Haskell-Cafe

Multiprocessor compiling.
by Matthew Roberts 01 Aug '04

01 Aug '04

It seems there is quite some interest in compiling code for multi-processor machines. As a research student, I am always looking for interesting projects to do. However, I am no haskell guru and have certainly never written a compiler. All the comments so far have been very interesting, but too many go over my head and I am not gettting a coherent view of what is going on. Let me try to tie this up. The basic computational model of functional languages seems inherantly parallilisable, but there are clearly many problems - and I don't really understand them. I just picked up the book on implementing the back end of a Haskell compiler and so I will eventually get there. For the meantime, and for all the others out there in my situation, could someone who knows tell us the fundamental reason it is hard to compile Haskell for multiple processor machines - in broad strokes. Cheers, Matt

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Hello and help request
by enrico.santoemma＠tin.it 01 Aug '04

01 Aug '04

Hello to everyone :) My name is Enrico, 40, and I write software for the industry at Beta 80 Group. After this short introduction, here is the help request: I'm managing the rewrite of an application, to port it to the 'classic' Java three-tiers architecture. Before I begin to feed the team, I want to see a fully functional prototype of the problem. I mean the app's functions, not the graphic. What I imagine is a data base of types and groups of functions. The idea is to study the problem, inject new functions while checking their coerence with the existing type infrastructure, and so on. In plain Java, I'd have wrote the Business Idea in informal language, extracted the types from it, assigned methods to types and then glued things together in some way. In Haskell I (should) have the opportunity to stay on the problem, decomposing it into sub-problems until I come to the soil. What I ask to this list is if and where Haskell is different from the object oriented way to decompose the problem. I'm very fresh on Haskell. Exactly... chapter 13 of SOE :) Are type classes different from Java classes? I think so, but I guess this means that one should ask different things to type classes, respect to what is being asked to Java classes. It is this difference that's unclear to me. Any help would be very appreciated Enrico

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Re: [Haskell-cafe] Re: humor
by Jon Cast 30 Jul '04

30 Jul '04

Sean Perry <sean.perry(a)intransa.com> wrote: > Gabriel Ebner wrote: > > enrico.santoemma(a)tin.it writes: > > > > > >>Well... more seriously, does someone have got links to applications with > >>visible source? > > > > > > The only one I know is darcs: http://abridgegame.org/darcs > > > > which is actually quite readable, even for a newbie. He does like the > '$' operator a bit much for my tastes though. Obviously you haven't realized the great beauty of $. You cannot like $ to much. foldr should be defined as follows: foldr f z [] = id $ z foldr f z (x:xn) = (f $ x) $ foldr f z xn etc. :) Jon Cast

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humor
by enrico.santoemma＠tin.it 30 Jul '04

30 Jul '04

When I met Java some time ago, I said to myself: "Java is a great language to write IDEs for the Java language". Now that I'm looking for Haskell source code (perhpas that there is another way to learn a language than to spy on others?), I'm tempted to say: "Haskell is a great language to write libraries for the Haskell language" Well... more seriously, does someone have got links to applications with visible source? Enrico Santoemma

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DiscreteMap
by Henning Thielemann 30 Jul '04

30 Jul '04

In addition to the former discussion: http://www.haskell.org/pipermail/haskell/2002-October/010629.html Has someone thought about a type class that provides a uniform interface to Array and FiniteMap? The difference to a general Function class is that a DiscreteMap could return its domain, that is the list of all of its keys/indices/arguments.

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lhaskell.vim syntax highlighting script
by Andrew Pimlott 29 Jul '04

29 Jul '04

haskell-cafe, you are listed as the maintainer of the vim haskell syntax highlighting script. :-) lhaskell.vim uses the tex.vim syntax script, which does "set iskeyword-=_". This makes editing haskell rather uncomfortable (eg, the '*' command doesn't work right). I don't know what breaks if you "set iskeyword+=_", but getting tex highlighting right is less important than haskell editing, so I suggest this patch. Andrew --- lhaskell.vim.orig 2004-07-29 16:48:39.000000000 -0700 +++ lhaskell.vim 2004-07-29 16:50:16.000000000 -0700 @@ -86,6 +86,8 @@ runtime! syntax/tex.vim unlet b:current_syntax endif + " This messes up tex a bit, but is better for Haskell. + set isk+=_ endif " Literate Haskell is Haskell in between text, so at least read Haskell

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Re: [Haskell-cafe] optimising for vector units
by MR K P SCHUPKE 29 Jul '04

29 Jul '04

Well I have to say the dataflow style of lazy programming made me think Haskell would be ideal for multi-processor use (and now HyperThreading is common most PCs have more than one processor from the code's point of view)... I was disappointed to find GHC only uses one thread, and therefore will only use one CPU. Vectorisation is much more limited than hyperthreading - as the instructions on each vector unit must be the same... The easiest implementation would be to add primitive vector types that map directly to the underlying SIMD operations. This is probably a good starting point - it would be nice to vectorise normal expressions, but that requires an optimisation search to find instructions that can be grouped together ... this becomes a lot easier if the primitives are supported as you just need to transform the code rather than dealing with non-portable assembly instructions. The problem is that different platforms support different SIMD style instructions... What would be really needed is a IEEE/ISO standard for vector instructions much like the current one for floating point. In the absence of such a standard, the best that can be done is to abstract vectorisation by word size and number of words, and supply a software implementation of all vector ops to use if the hardware does not support certain primitives. A futher point is that for the compiler to know the vector size, you would have to resort to type level naturals... something like: data Nil data Suc x = Suc x type Four = Suc (Suc (Suc (Suc Nil))) myFn :: Vector Four Word16 Of course this would need to be integrated with the compiler. As an interim measure a C-library providing primitive operations on vectors could be written and used via the FFI. Keean.

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Re: [Haskell-cafe] why is Prelude.^ so convoluted?
by blaetterrascheln＠web.de 29 Jul '04

29 Jul '04

> x ^ n = if even n then y*y else y*y*x where y = x ^ (n `quot` 2) x ^ n | n>0 = if even n then y*y else y*y*x where y = x ^ (n `quot` 2) ________________________________________________________________ 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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Typeclass problem
by Mark T.B. Carroll 29 Jul '04

29 Jul '04

I have a little programme that doesn't compile: module Example where class (Show c, Ord c, Bounded c) => MyClass c showThings :: MyClass c => c -> (String, String) showThings x = let foo = maxBound :: c in (show x, show foo) If I change that second-to-last line to, let foo = max x maxBound then it compiles. However, it's clearly silly to use "max" just to make the type of the maxBound be the same type as the x. (I'm assuming that the Ord and the Bounded instances of the type are sensibly consistent.) What should I be writing if I want foo to be the maxBound applied to the type that x is? -- Mark

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why is Prelude.^ so convoluted?
by blaetterrascheln＠web.de 29 Jul '04

29 Jul '04

{- (^) :: (Num a, Integral b) => a -> b -> a x ^ 0 = 1 x ^ n | n > 0 = f x (n-1) x where f _ 0 y = y f x n y = g x n where g x n | even n = g (x*x) (n`quot`2) | otherwise = f x (n-1) (x*y) _ ^ _ = error "Prelude.^: negative exponent" -} -- Is (^) :: (Num a, Integral b) => a -> b -> a x ^ 0 = 1 x ^ n = if even n then y*y else y*y*x where y = x ^ (n `quot` 2) _ ^ _ = error "negative exponent" -- not good enough? ________________________________________________________________ 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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