- Haskell-Cafe - Haskell.org

Bracketless branch if, sugar to taste...
by Alex Ferguson 13 Feb '03

13 Feb '03

Yes indeed, one can further "sugar" Keith's suggestion to eliminate the need for brackets around the branches. Though as this means using an infix operator then and else, with corresponding mangling of the lexical appearance of same, this becomes increasingly a matter of taste (or perhaps, in need of sound dental advice). Example: ifM (return (1==1)) `then_` print (2+3) `else_` print (3+4) Of course, the type errors are going to start looking more and more mysterious if you get 'em in the wrong place... Cheers, Alex. ________ infix 4 `then_` infix 5 `else_` data Branches a = Branches a a then_ :: (a->a->a) -> Branches a -> a then_ sel (Branches t e) = sel t e else_ :: a->a->Branches a else_ t e = Branches t e iff b t e = if b then t else e ifM b t e = do test <- b if test then t else e

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MArray and newSTUArray
by Dean Herington 13 Feb '03

13 Feb '03

The MArray class in Data.Array.MArray is a very nice abstraction. However, when creating an array whose type partakes of MArray, say STUArray, I find myself defining and using a type-specific creation function, such as: newSTUArray :: (MArray (STUArray s) e (ST s), Ix i) => (i, i) -> e -> ST s (STUArray s i e) newSTUArray = newArray so that I don't have to give a complicated type declaration for each use of `newArray` that creates an STUArray. 1. Is there a better (more concise/convenient) way to provide the necessary type information? 2. If not, should functions such as `newSTUArray` be provided in the libraries? -- Dean

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RE: a monadic if or case?
by Kevin Millikin 13 Feb '03

13 Feb '03

On Thursday, February 13, 2003 8:33 AM, Arjan van IJzendoorn [SMTP:afie@cs.uu.nl] wrote: > Not with the syntactic sugar of 'if'. > But you can write [warning: untested code ahead] > > ifM :: IO Bool -> IO a -> IO a -> IO a > ifM test yes no = do > b <- test > if b then yes else no I had ifM :: Monad m => m Bool -> m a -> m a -> m a ifM tst thn els = do b <- tst if b then thn else els And I just tested it. ---- Kevin S. Millikin Architecture Technology Corporation Research Scientist Specialists in Computer Architecture kmillikin(a)atcorp.com http://www.atcorp.com

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Re: Learning Haskell moved
by Matthew Donadio 13 Feb '03

13 Feb '03

>> I would add some significant papers, such as John Hughes' >> "Why functional programming matters", etc. > >I've added that paper to the introduction. Other suggestions are welcome. "Conception, Evolution, and Application of Functional Programming Languages", Paul Hudak, ACM Computing Surveys, Volume 21, Number 3, pp.359-411, 1989 This would probably be good, too. --Matthew Donadio (m.p.donadio(a)ieee.org)

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Pattern matching, implict par. question
by Jorge Adriano 13 Feb '03

13 Feb '03

Hello, When trying type CTPar = ([Double],Int,Int) ctPar ::(?ctPar::CTPar)=>CTPar ctPar@(us,n,j) = ?ctPar I got this error message in ghci is: " Illegal overloaded type signature(s) in a binding group for ctPar, us, n, j that falls under the monomorphism restriction When generalising the type(s) for ctPar, us, n, j Failed, modules loaded: CrossTypeOps." Should the monomorphis restriction really apply here? The values of us,j,n do depend on the context, but not their types (right?). J.A.

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ANNOUNCE: Learning Haskell portal, version 0.1
by Arjan van IJzendoorn 13 Feb '03

13 Feb '03

Hello all, Often we see messages from people who want to learn Haskell (something we applaud), but don't know where to begin. The Haskell homepage offers a lot of information, links and papers, but there is no page aimed specifically at beginning programmers. That's why I started to collect some links and put them on one single webpage. I thought about what the target audience would be interested in: getting an implementation, buying a book, reading course material, looking up functions in references and so on. The page I have now is a first start and I will work on it more. I've probably overseen many good tutorials, maybe a book here or there, listed an incorrect pro or con of an implementation and what not. Please tell me about it. If you have useful contributions ( nice slides, exercises with(out) solutions, some handout you give to your students which everyone could benefit from ) tell me about it, too. Enough talk: http://www.cs.uu.nl/~afie/haskell/LearningHaskell.html Cheers, Arjan PS: As one of the people in the Helium team I would not recommend beginners to use Helium yet. The absence of classes which leads to simpler types and messages is just not compatible with the text books and other teaching materials. Our plan is to add enough support for classes so that you can use the books without modification. This can be expected this summer. From that moment on, I will definitely recommend Helium to beginners since the feedback from the system is really great.

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RE: SPECIALIZE pragma
by Simon Peyton-Jones 13 Feb '03

13 Feb '03

If 'g' is defined in the same module, yes. Simon | -----Original Message----- | From: Sengan.Baring-Gould(a)nsc.com [mailto:Sengan.Baring-Gould@nsc.com] | Sent: 12 February 2003 23:45 | To: haskell-cafe(a)haskell.org | Subject: SPECIALIZE pragma | | Hi, | | If I have {-# SPECIALIZE f ... #-}, | and I have f x y = ... (g x) ..., | will g also be specialized? | | Thanks, | | Sengan | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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Good Tutorial to start with?
by Daniel Jian 13 Feb '03

13 Feb '03

Dear All, I use a lot of C++, a little bit of Java, and some other programming languages. But none of them is a functional language. I would like to learn Haskell as my first introduction to FP. Do any of you know a good tutorial for me to start with? FYI, it is easier for me to learn a new language by looking at the source code first, and then the explanation of that code. I browsed through the internet for quite a while, but still I could not find any tutorial that is not tediously long in discussion. Thanks! best regards, Daniel Jian __________________________________________________ Do you Yahoo!? Yahoo! Shopping - Send Flowers for Valentine's Day http://shopping.yahoo.com

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SPECIALIZE pragma
by Sengan.Baring-Gould＠nsc.com 12 Feb '03

12 Feb '03

Hi, If I have {-# SPECIALIZE f ... #-}, and I have f x y = ... (g x) ..., will g also be specialized? Thanks, Sengan

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Beginner help
by JJ 12 Feb '03

12 Feb '03

(My apologies if this is off topic) Functional programming is completely new to me. I've been doing imperative programming for quite a while. >From my perspective, the learning curve for Haskell seems to be near vertical. I've read several things on the web, and am working my way through The Haskell School of Expression. Any words of wisdom? ADVthanksANCE, JJ Be Kind, Be Careful, Be Yourself

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