On 07/07/2012 05:06, Favonia wrote:
Hi all,
Recently I am tuning one of our incomplete libraries that uses FFI. After dumping the interface file I realized strictness/demand analysis failed for imported foreign functions---that is, they are not inferred to be strict in their arguments. In my naive understanding all imported foreign functions are strict! Here's a minimum example (with GHC 7.4.2):
{-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign.C foreign import ccall unsafe "sin" sin' :: CDouble -> CDouble
where in the interface file the function sin' will have strictness U(L) (meaning Unpackable(Lazy)).
This is fine - it means the CDouble is unpacked into its unboxed Double# component. An unboxed value is always represented by L in strictness signatures. Cheers, Simon