November 2003 - Glasgow-haskell-users

Foreign Function Interface (FFI)
by Rafael Martinez Torres 28 Nov '03

28 Nov '03

HI: Reading Haskell 98 FFI report, one question arised: Imported and declared a foreign function , via foreign import ccall foo:: IO(CInt) Is it guaranteed to be executed in atomic way ? I mean , should it block the whole STG system ? Idea: To implement a monitor , in a "external context" , and threads around him to access it, bypassing the Mvar paramter-pass among them...

2 2

Pestilential behaviour of gcc3.3 on Macs
by George Russell 27 Nov '03

27 Nov '03

Yes I know this is really Apple's fault, but according to http://developer.apple.com/documentation/ReleaseNotes/DeveloperTools/GCC3.h… > The GCC 3.3 preprocessor inserts a new pragma, #pragma GCC set_debug_pwd, as part > of the new Distributed Builds feature. (See below.) This may surprise tools and > scripts that depended on the exact form of preprocessed output from GCC. These > scripts should be rewritten to ignore unrecognized pragmas. Would it be possible for GHC to ignore this line? Otherwise ghc -cpp is going to fall over with gcc3.3 on Macs. Of course in the ideal world I know we should be using Template Haskell.

2 1

RE: Time profiling question.
by Simon Marlow 26 Nov '03

26 Nov '03

> Let me ask this question in the abstract, lest I embarrass myself > publicly with my shoddy code: > > Suppose I find that -p style profiling with -auto-all attributes the > majority of the cost of my program to a single function. > Naturally, I'd > like to refine this somewhat. So I add additional cost centres as > follows: > > f a1 ... an > = e > where > d1 = {-# SCC "d1" #-} e1 > ... > d1 = {-# SCC "dn" #-} e1 > > I find it's still attributing almost all of the cost to the > original CC > (f), so I add another SCC, before the RHS. And it _still_ attributes > the same amount to f, and effectively nothing to the body CC. Sounds like it might be a bug. There are known problems in the attributions of costs in the profiling system, though: in particular some transformations in the simplifier can affect the cost attribution. This might be what's happening, but it would be nice to see an example so we can investigate. Any chance you can boil down your code? Cheers, Simon

1 0

RE: specializing on existentially quantified data types
by Simon Peyton-Jones 25 Nov '03

25 Nov '03

Thanks Lennart -- you are quite right. That comes of sending email before having my morning coffee. Yes you can make the specialised foo', but it'll never be called -- unless you call foo on a *particular* data structure and inlining removes the MkC wrapper etc. GHC is, of course, magical, but not quite that magical. You could do a run-time type test (via class Typeable, making Typeable a superclass of C), and then you *would* be able to call the specialised foo --- but at the cost of the test. Which is, I guess, not unreasonable. Simon | -----Original Message----- | From: Lennart Augustsson [mailto:lennart@augustsson.net] | Sent: 25 November 2003 09:08 | To: Simon Peyton-Jones | Cc: Hal Daume III; GHC Users Mailing List | Subject: Re: specializing on existentially quantified data types | | I don't know how specialised code works in ghc, so I have to ask. | Does this actually work? | The type of x is never known at the foo' call site, so the specialised | version of foo' will only be called if ghc does a run time test on the | type when invoking foo'. Does it do that? | | -- Lennart | | Simon Peyton-Jones wrote: | > | class C a where ... | > | data MkC = forall a . C a => MkC a | > | | > | foo :: MkC -> ... | > | | > | and I want to specialize foo for when the 'a' in the MkC is, say, Int. | > Is | > | this possible? | > | > Not directly. But you can say | > | > foo (MkC x) = foo' x | > | > foo' :: forall a. C a => a -> ... | > foo' x = ... | > {-# SPECIALISE foo' :: Int -> ... #-} | > | > There's no built-in mechanism I'm afraid. | > | > Simon | > | > _______________________________________________ | > Glasgow-haskell-users mailing list | > Glasgow-haskell-users(a)haskell.org | > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users | > | |

2 1

RE: specializing on existentially quantified data types
by Simon Peyton-Jones 25 Nov '03

25 Nov '03

| class C a where ... | data MkC = forall a . C a => MkC a | | foo :: MkC -> ... | | and I want to specialize foo for when the 'a' in the MkC is, say, Int. Is | this possible? Not directly. But you can say foo (MkC x) = foo' x foo' :: forall a. C a => a -> ... foo' x = ... {-# SPECIALISE foo' :: Int -> ... #-} There's no built-in mechanism I'm afraid. Simon

2 1

specializing on existentially quantified data types
by Hal Daume III 24 Nov '03

24 Nov '03

Hi all, Suppose you have: class C a where ... data MkC = forall a . C a => MkC a foo :: MkC -> ... and I want to specialize foo for when the 'a' in the MkC is, say, Int. Is this possible? -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume

1 0

HTk + ghc6.01
by George Russell 24 Nov '03

24 Nov '03

Binaries for HTk (a Haskell graphics package that uses HTk) for ghc6.01 on Linux, Solaris, Windows and FreeBSD are now available from the HTk page: http://www.informatik.uni-bremen.de/htk/ Many thanks to Guy Coleman for the FreeBSD package.

1 0

List - Mutable List
by Rafael Martinez Torres 21 Nov '03

21 Nov '03

Hi: Given the classes IArray,Marray instance IArray Array.Array instance Marray IOArray e IO I'm searching for some think like MLists ( Stands for Mutable-Lists ) Is there some thing so ? I need it to implement a MQueue ... (Mutable Queue )

2 1

RE: auto cost centres for where decls
by Simon Marlow 21 Nov '03

21 Nov '03

> I have a large function with a lot of local definitions I would like > indepdent cost centres for, however, since the local definitions arn't > top-level auto-all doesn't catch them. is there some short cut to > declare a whole list of decls should have cost centres? > > I was thinking something like > > foo = ... where {-# SCC "foo" #-} > baz = ... > bar = ... > > would cause baz and bar to have cost centres named "foo.baz" and > "foo.bar" That's a good idea, but we probably won't get around to it until we do the next profiling overhaul. So that we don't lose suggestions like this, it's a good idea to add them to the feature request tracker, here: http://sourceforge.net/tracker/?group_id=8032&atid=358032 (this is the "Request a Feature" link on GHC's homepage). Cheers, Simon

1 0

auto cost centres for where decls
by John Meacham 19 Nov '03

19 Nov '03

I have a large function with a lot of local definitions I would like indepdent cost centres for, however, since the local definitions arn't top-level auto-all doesn't catch them. is there some short cut to declare a whole list of decls should have cost centres? I was thinking something like foo = ... where {-# SCC "foo" #-} baz = ... bar = ... would cause baz and bar to have cost centres named "foo.baz" and "foo.bar" John -- --------------------------------------------------------------------------- John Meacham - California Institute of Technology, Alum. - john(a)foo.net ---------------------------------------------------------------------------

1 0