January 2002 - Glasgow-haskell-users

Re: Packages
by Marcin 'Qrczak' Kowalczyk 19 Jan '02

19 Jan '02

Sat, 19 Jan 2002 10:10:22 -0500, Mark Conway Wirt <mark(a)ArsConcero.org> pisze: > I ran into this problem with the mysql DB interface. If you change > "qforeign" to "qforeign-curses" in the first line of the .hi file, it > should work. It won't work unless I changed it each time a module from a different package imports this. And it's wrong: the file belongs to qforeign, only it's not installed as qforeign yet. Anyway, it was an error with some versions of ghc near 5.0, it's a warning now, but I want to get rid of the warning. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ QRCZAK

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Packages
by Marcin 'Qrczak' Kowalczyk 19 Jan '02

19 Jan '02

QForeign under ghc consists of several packages with some interdependencies. I'm getting warnings during compilation, e.g.: /usr/local/bin/ghc -c -O -Wall -fglasgow-exts -package lang -package data -package concurrent -package posix -iexamples -ilib -Iexamples -Ilib -package-name qforeign-curses examples/Curses.hs Curses.hsc:1: Warning: Module `QIntegral' is located in package `qforeign-curses' but its interface file claims it is part of package `qforeign' I understand what it means but I don't know how to fix it. QIntegral should be in package qforeign, but's found by -ilib during compilation of other modules which use it because it's not installed yet! Please help. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ QRCZAK

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Bilgilendirme Forumu
by HostingTalk Web 19 Jan '02

19 Jan '02

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Re: question about kinds
by Ashley Yakeley 18 Jan '02

18 Jan '02

At 2002-01-18 13:19, Hal Daume III wrote: >In theory, I could write: > >class Traversable d a where > traverse :: d a -> (Maybe a, [d a]) > >instance Traversable Tree a where > traverse (Leaf a) = (Just a, []) > traverse (Branch t1 t2) = (Nothing, [t1,t2]) > >instance Traversable [] a where > traverse [] = (Nothing, []) > traverse (x:xs) = (Just x, [xs]) > >instance (Traversable d (e a), Traversable e a) => Traversable d (e >a) where > traverse = ... > >but then both ghc and hugs complain about overlapping instances, even with >-fallow-overlapping-instances/-fallow-undecidable-instances in ghc and +o >in hugs. Try this: class Traversable t a where -- note no fundep traverse :: t -> (Maybe a, [t]) instance Traversable (Tree a) a where traverse (Leaf a) = (Just a, []) traverse (Branch t1 t2) = (Nothing, [t1,t2]) instance Traversable [a] a where traverse [] = (Nothing, []) traverse (x:xs) = (Just x, [xs]) instance (Traversable (d (e a)) (e a), Traversable (e a) a) => Traversable (d (e a)) a where traverse = ... ...or even, more generally... instance (Traversable a b, Traversable b c) => Traversable a c where traverse = ... -- Ashley Yakeley, Seattle WA

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Re: question about kinds
by Ashley Yakeley 18 Jan '02

18 Jan '02

At 2002-01-18 13:10, Hal Daume III wrote: >Now, I want to say that if some data type 'd' is Traversable and another >data type 'e' is Traversable, then the "combined data type" is >Traversable. That is, for example, I want to say that a Tree of Lists is >traversable, or that a List of Trees, or a List of Lists is traversable. If the Tree type constructor is Traversable, then it's Traversable no matter what it's applied to. You've provided a instance for traversing "Trees of anything", it's going to overlap with any instance for "Trees of Lists". -- Ashley Yakeley, Seattle WA

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question about kinds
by Hal Daume III 18 Jan '02

18 Jan '02

I have the following definition: > class Traversable d where > traverse :: d a -> (Maybe a, [d a]) And the standard binary tree data type: > data Tree a = Branch (Tree a) (Tree a) > | Leaf a I can define both Tree and [] to be instances of Traversable: > instance Traversable Tree where > traverse (Leaf a) = (Just a, []) > traverse (Branch t1 t2) = (Nothing, [t1,t2]) > instance Traversable [] where > traverse [] = (Nothing, []) > traverse (x:xs) = (Just x, [xs]) Now, I want to say that if some data type 'd' is Traversable and another data type 'e' is Traversable, then the "combined data type" is Traversable. That is, for example, I want to say that a Tree of Lists is traversable, or that a List of Trees, or a List of Lists is traversable. But I can say neither: > instance Traversable (Tree []) where ... or: > instance (Traversable a, Traversable b) => Traversable (a b) where .. Because of the obvious kind errors. What I suppose I need is some sort of lambda expansion over kinds, so I could say: > instance (Traversable a, Traversable b) => Traversable (\x -> a b x) or something like that. Obviously this doesn't exist. How can I get around this? - Hal -- Hal Daume III "Computer science is no more about computers | hdaume(a)isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume

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bug report trouble?
by Feuer 17 Jan '02

17 Jan '02

I sent a bug report recently to glasgow-haskell-bugs(a)haskell.org. I have not seen any response to that message, or in fact any (non-spam) messages on the list after it. Is this still the right place to send bug reports? If not, where should I send it? David Feuer

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Re: FFI
by Sven Panne 16 Jan '02

16 Jan '02

Manuel M. T. Chakravarty wrote: > I think, there are five options: > > * H/Direct (you mentioned that already) > * GreenCard (ditto) > * C->Haskell > http://www.cse.unsw.edu.au/~chak/haskell/c2hs/ > * hsc2hs (comes with GHC) > * Plain FFI Plus: * Write your own IDL compiler for a given formal description of an API This sounds a little bit like overkill at first, but at least for my never-ending HOpenGL project it makes a lot of sense: There is a rather large (maintained!) description of the OpenGL API (plus a few more things like GLX) at http://oss.sgi.com/cgi-bin/cvsweb.cgi/projects/ogl-sample/main/doc/registry… which could be used to generate header files, network code for GLX, stubs, etc. (and of course a low-level Haskell binding :-) Of course one could hack H/Direct in a way that it understands these .spec files, but a home-grown compiler was the easier and more tunable way. I hope to release a new version of HOpenGL based on this "soon". :-} SimonM has written a small program/hack to auto-generate something for GTK+, IIRC, so I'm probably not alone on this route... I agree with Koen on his points: * Plain FFI plus a few combinators is not so bad at all for small to medium-sized bindings. Only the mapping of Haskell enumerations to C enums/ints and back is *really* boring... * No tool whatever generates a Haskellish binding one wants to present to an end user, so a wrapper around the lower Haskell level is necessary, anyway. Manuel: Could the results/opinions of this thread added somewhere? I'm not sure where, the libraries/tools page of haskell.org is a possibility, but your page could be used, too. Cheers, S. -- Sven Panne Fon: +49/89/99567000 Fax: +49/89/99567461 BetaResearch GmbH, Betastr. 1, D-85774 Unterfoehring mailto:Sven_Panne@BetaResearch.de http://www.betaresearch.de

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FFI
by Mark Conway Wirt 14 Jan '02

14 Jan '02

I'm looking for opinions as to the best way to do a C (or C++) foreign interface to GHC haskell code. It looks like there are three options. Greencard has been around for a while, but it looks as if it's more-or-less deprecated now; I don't see many people talking about it anymore. Unless I'm wrong about this (and if I am, please disabuse me of this bias), it doesn't sound like the obvious choice. That leaves me with GHC's FFI and hdirect. I've played around a bit with hdirect in ghc-5.02 and it works. I haven't really looked at the native FFI (beyond reading some manual pages), so I'm not really sure what hdirect provides that the FFI doesn't. From a cursory glance it looks like hdirect's ihc is useful for auto-generating interface files, but it may be over-kill for my smallish project. Any feedback or personal biases are welcomed. Thanks, --Mark

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Multiply Recursive Modules
by George Russell 14 Jan '02

14 Jan '02

Writing .hi-boot files is a pain, and "the works" (allegedly) containing a compiler which does mutually recursive modules properly seem permanently gummed up. Therefore may I suggest a new .hs-boot suffix which compiles Haskell to produce just a .hi-boot file? I already have two .hs-boot files (except I call them .boot.hs to make ghc happy) and they seem to work reasonably well.

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