RE: Checking for WHNF (a horrible naughty thing)
On 23 November 2005 18:29, Sigbjorn Finne wrote:
The appended snippet might help..
--sigbjorn
-- whnf.hs
import Foreign.StablePtr
import System.IO.Unsafe
isWHNF :: a - Bool
isWHNF a = unsafePerformIO $ do
stl - newStablePtr a
rc - isWhnf stl
freeStablePtr stl
return (rc /= 0)
foreign import ccall safe isWhnf isWhnf :: StablePtr a - IO Int
/* whnf.c */
#include Rts.h
int
isWhnf(StgStablePtr st)
{
StgClosure* c = (StgClosure*)(stable_ptr_table[(StgWord)st].addr);
return !(closure_THUNK(c));
}
using deRefStablePtr() would be slightly better. Also, you should
consider whether you want indirections to be counted as WHNF or not.
Also, I think you can make that foreign import unsafe (safe will be
slow). For more speed you could implement it directly as a primitive.
Cheers,
Simon
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Checking for WHNF (a horrible naughty thing)
I would like to do a horrible naughty thing (which I promise never to expose to the world). I would like to tell whether a term is in WHNF, without forcing evaluation of that term. Something like: isWHNF :: a - Bool Is there a way of doing this? I can fake it with an IORef and much unsafeness, but I'm wondering if there's a safe-but-ugly way of doing the test in GHC. If you're curious, I'm trying to compact exactly the evaluated spine of a list without changing the list's laziness in any way. It remains to be seen whether this is even vaguely a good idea. :-) -Jan-Willem Maessen ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Checking for WHNF (a horrible naughty thing)
The appended snippet might help..
--sigbjorn
-- whnf.hs
import Foreign.StablePtr
import System.IO.Unsafe
isWHNF :: a - Bool
isWHNF a = unsafePerformIO $ do
stl - newStablePtr a
rc - isWhnf stl
freeStablePtr stl
return (rc /= 0)
foreign import ccall safe isWhnf isWhnf :: StablePtr a - IO Int
/* whnf.c */
#include Rts.h
int
isWhnf(StgStablePtr st)
{
StgClosure* c = (StgClosure*)(stable_ptr_table[(StgWord)st].addr);
return !(closure_THUNK(c));
}
- Original Message -
From: Jan-Willem Maessen [EMAIL PROTECTED]
To: glasgow-haskell-users glasgow-haskell-users@haskell.org
Sent: Wednesday, November 23, 2005 08:10
Subject: Checking for WHNF (a horrible naughty thing)
I would like to do a horrible naughty thing (which I promise never to
expose to the world). I would like to tell whether a term is in
WHNF, without forcing evaluation of that term. Something like:
isWHNF :: a - Bool
Is there a way of doing this? I can fake it with an IORef and much
unsafeness, but I'm wondering if there's a safe-but-ugly way of doing
the test in GHC.
If you're curious, I'm trying to compact exactly the evaluated spine
of a list without changing the list's laziness in any way. It
remains to be seen whether this is even vaguely a good idea. :-)
-Jan-Willem Maessen
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Glasgow-haskell-users@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
___
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