Imported foreign functions should be strict
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)). Regards, Favonia
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
I see. Thanks for the response! Perhaps it is better for the pretty
printer to print out "U(S)" instead?
Regards,
Favonia
On Tue, Jul 10, 2012 at 3:57 AM, Simon Marlow
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
On Thu, Jul 12, 2012 at 11:29 AM, Favonia
I see. Thanks for the response! Perhaps it is better for the pretty printer to print out "U(S)" instead?
Regards, Favonia
I'd love to see a cheat sheet documenting the strictness output. It confuses me every time, even when I make the effort to read the source code that generates the demand signature! -- Johan
participants (3)
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Favonia -
Johan Tibell -
Simon Marlow