Hi Maciej, Thanks to have take some time to read this code. I rewrite using your comments: import Foreign import Foreign.C data CStruct = CStruct (CULong, CULong) instance Storable CStruct where sizeOf _ = 2*sizeOf (undefined::CULong) alignment _ = alignment (undefined::CULong) test = with (CStruct (1,1)) (\ptr -> return ()) The class Storable does not need to make your own peek and poke method (the class provide a default implementation). But with, i have still the behavior when I try this code in ghci. Please, can you test this code and tell me why ghci stay blocked after executing the method test. BR Marco 2010/2/6 Maciej Piechotka <uzytkownik2@gmail.com>
On Sat, 2010-02-06 at 12:28 +0100, Marco De Oliveira wrote:
Hi,
I try to initialize a C struct using the FFI API and ghc stays blocked when I execute my code (and I got sometimes the error "out of memory"). I do not understand, I do not find any mistake in my code:
{-# OPTIONS -XTypeSynonymInstances #-}
import Foreign.C.Types import Foreign.Marshal.Alloc import Foreign.Ptr import Foreign.Storable
It can be written as: import Foreign import Foreign.C
type CStruct = (CULong, CULong)
I guess that you may want to use newtype or data rather then type to avoid clashes (and have just 98 + FFI):
newtype CStruct = CStruct (CULong, CULong) data CStruct = CStruct CULong CULong
instance Storable CStruct where sizeOf _ = 2*sizeOf (undefined::CULong) alignment _ = alignment (undefined::CULong)
To begin with - where's peek and poke?
test = alloca (\pStruct -> do poke pStruct ( (fromIntegral 1)::CULong, (fromIntegral 1)::CULong ) )
If you just do this at the beginning you may want to use with (notation as with newtype/data):
with (CStruct (1, 1)) (\ptr -> ...)
Also is main = test?
Thanks for your help.
Marco
Regards
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