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RE: Implementing forward refs in monadic assembler and interprete r
by Ashley Yakeley 02 Dec '02

02 Dec '02

At 2002-12-02 00:37, Simon Peyton-Jones wrote: >Main things in the next major release are > mdo > Template Haskell Can mdo be done in TH? It would be nice if there were some kind of macro system for this sort of thing; I know there's also a syntax for Arrows that requires a preprocessor... -- Ashley Yakeley, Seattle WA

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RE: Implementing forward refs in monadic assembler and interprete r
by Simon Peyton-Jones 02 Dec '02

02 Dec '02

| For the moment I've chosen to do the mdo desugaring manually instead | of moving to the CVS ghc (or exclusively using Hugs.) Will mdo be in | the next release? (That's 5.04.2, I think -- though I've recently | been confused about GHC releases.) The relevant revision to Lex.lhs | is pretty recent and doesn't seem to be on ghc-5-04-branch. mdo won't be in 5.04.2; these patch releases are meant to be bug fixes only. As I mentioned in an earlier message, we are undecided about when to invest the effort to make another major release. The more people that yell, the sooner we will do it! Main things in the next major release are mdo Template Haskell a fairly major fix to the newtype-deriving mechanism (it's a bit broken in 5.04) Simon

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someone help me
by Nuno Silva 30 Nov '02

30 Nov '02

I'm relatively new to haskell and have some questions: 1- I want to convert an integer to a char( if I say prelude> convert 4 ... it should return prelude> '4') 2- and vice versa? 3- I want to define a function that stores in a variable the following... pretended: (Int,Int,Int,Int) give :: IO Int give = randomRIO (0,9) main = do k <- (give,give,give,give) actualy this isn't possible. but can someone please tell how to do this??? thank you very much --------------------------------- Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now

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RE: Implementing forward refs in monadic assembler and interprete r
by Erkok, Levent 29 Nov '02

29 Nov '02

> For the moment I've chosen to do the mdo desugaring manually instead > of moving to the CVS ghc (or exclusively using Hugs.) Will mdo be in > the next release? (That's 5.04.2, I think -- though I've recently > been confused about GHC releases.) The relevant revision to Lex.lhs > is pretty recent and doesn't seem to be on ghc-5-04-branch. The current CVS-head for GHC contains the mdo implementation (thanks to Simon PJ). I'm not sure what they're going to call it (i.e. 5.04.2, or 5.05, etc.), but the next release will have mdo for sure. I don't know when they'll make a new release though, maybe one of the Simon's can comment on that? -Levent.

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Re: Implementing forward refs in monadic assembler and interprete r
by Mike Gunter 29 Nov '02

29 Nov '02

Thank to all who replied. After giving up on continuations (which make everything but forward branches seductively easy), I settled on something with the following interface: > class MonadGoto lbl gm | gm -> lbl where > liftG :: Monad m => m () -> gm m () > label :: Monad m => gm m lbl > gotoIf :: Monad m => m Bool -> lbl -> gm m () Note that, unlike a monad transformer, only ()-producing computations can be embedded. This limitation reflects the problem of def-use across basic-block boundaries. Of course, computations in the embedded monad can be done there, then lifted, e.g.: > ;top <- label > ; ... > ; liftG (do v <- m1 > ; ... > ; m2 v > ; ...) > ; brPositive r3 top > ; ... I've implemented MonadGoto as > newtype GotoT m a = GotoT { unGotoT :: WriterT [GotoLbldT m ()] LblSupply a } > > data GotoLbldT m a = Label !Lbl > | GotoIf (m Bool) !Lbl > | Inner (m a) > > wrL = GotoT . tell . (:[]) > instance MonadGoto Lbl GotoT where > liftG = wrL . Inner > label = GotoT $ lift fromSupply >>= \l -> tell [Label l] >> return l > gotoIf p l = wrL $ GotoIf p l where GotoLbldT gets converted to > data GotoLbldRunT m a = ThenLabel { before :: m (), next :: GotoLbldRunT m a, labelLbl :: !Lbl } > | ThenGotoIf { before :: m (), next :: GotoLbldRunT m a > , gotoPred :: m Bool, gotoLbl :: !Lbl } > | Tail (m a) which can then be run > type JumpArray m v = [(Lbl, m v)] > runGM :: Monad m => JumpArray m v -> GotoLbldRunT m v -> (JumpArray m v, m v) . My Verilog has delayed branches (because that's the easy thing to do.) So, I implemented a DelayedGotoT which provides for delayed branches by shuffling the "GotoLbldT"s and using a StateT to save the result of the gotoPred evaluation. "Erkok, Levent" <levent.erkok(a)intel.com> writes: > You need a fairly recent version of Hugs to run this > example, November 2002 release would do (try with -98). For ghc, you need > the CVS version, or wait till the next release. As far as I know, no other > implementation supports mdo, nor there are any plans for it. For the moment I've chosen to do the mdo desugaring manually instead of moving to the CVS ghc (or exclusively using Hugs.) Will mdo be in the next release? (That's 5.04.2, I think -- though I've recently been confused about GHC releases.) The relevant revision to Lex.lhs is pretty recent and doesn't seem to be on ghc-5-04-branch. thanks, mike

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Merhaba;
by www.erotikmagaza.com 26 Nov '02

26 Nov '02

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Random Color
by Mike T. Machenry 21 Nov '02

21 Nov '02

I am trying to construct an infinate list of pairs of random colors. I am hung up on getting a random color. I have: data Color = Blue | Red | Green deriving (Eq, Ord, Show) am I supposed to instantiate a Random class instance from color? I am not sure exactly how the random number generator works. Is this the best way to go about it? Should I instead get a random Integer index of an array of Colors? thanks, -mike

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Re: Sets
by Christopher Milton 19 Nov '02

19 Nov '02

This might be of some help, circa Haskell 1.2, SetMap.hs - sets and maps in Haskell Author: Nick North ftp://ftp.cs.chalmers.se/pub/haskell/library/SetMap.hs Chris ===== Christopher Milton cmiltonperl(a)yahoo.com __________________________________________________ Do you Yahoo!? Yahoo! Web Hosting - Let the expert host your site http://webhosting.yahoo.com

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newbie question re linear algebra in Haskell
by Jeff Austin 19 Nov '02

19 Nov '02

I'm a complete newcomer to Haskell, having learned about only recently. I'm intrigued by the possibility of in using it for numerical applications, specifically linear algebra. I understand that (at least in its present state) Haskell 98 isn't competitive with imperative languages when it comes to primitive matrix-vector operations, which often rely on destructive updating. It strikes me that one approach that takes advantage of the strengths of both paradigms would be create an imperative subsystem to handle primitive operations, then create a functional matrix algebra layer on top of it. Based on my very limited understanding of Haskell, I envision a linear algebra library which would work something like this: (1) Create a wrapper for the standard BLAS library. Since an optimized BLAS is available for various architectures with the same interface, this would provide a way of optimizing the library for a particular architecture. (2) Encapsulate this (using a monad?) in a way that provides safe access to the imperative routines from Haskell. (3) Using this as a foundation, define a matrix algebra in a "smart" way which avoids redundant evaluations. For instance, if A is an arbitrary invertible matrix, we know that A - A = 0 A + 0 = A A * Indentity = A A * inverse A = Identity so if we write an expression like "X = A * inverse A + B - B" we should expect our library to compute the correct result, "Identity" without actually performing any inversion, multiplication or elementwise matrix addition. (4) Create a Haskell module which exposes a pure functional interface, hiding the imperative subsystem from the user. My questions are: (a) Is this idea sound? (b) Has someone already done this? (c) Is there a better way of doing efficient linear algebra in Haskell? I would greatly appreciate any advice in this regard. --Jeff Austin

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Network objects (was RE: deriving (...))
by Garner, Robin 19 Nov '02

19 Nov '02

> BTW, those typed returns on sockets that Shawn mentioned sounded > interesting. IIRC Modula-3 also had some approach to worrying about data > exchange between older and newer versions of the same program. Modula-3 (actually the Network Objects library) used subtyping to handle this. Successive versions of an interface are declared as subtypes of the previous version, and the type system will resolve a network object binding to the appropriate version. Hard to see how this could be done in a purely functional setting. robin

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