Am Mittwoch, 20. Dezember 2006 16:10 schrieb Axel Jantsch:
[...] My simplified codes is as follows:
f :: InparT -> IO CInt f inPar = do inP <- malloc poke inP inPar
r <- cfun inP
free inP return r
This can be simplified to 'flip with cFun' (malloc/free pair => alloca, alloca/poke => with).
[...] So even if I make cfun pure (which it is), the enclosing function f is not.
This depends on the viewpoint: Unless malloc fails, f will return the same value for the same argument, so it can be considered pure.
Shall I pretend f is pure and wrap it into unsafePerformIO?
You can do this, but you still depend on the compiler/interpreter not doing any funny transformations which could duplicate an application of f. I don't think that this will be a problem in practice, but to be on the safe side you could memoize f or cFun and perhaps even a 1-element cache might be enough to avoid all this trickery. Cheers, S.