Malcolm Wallace wrote:
foreign import ccall "math.h signgam" signgamC :: IO Int
signgam is an "int" variable, but this assumes that it is a function of type "int signgam(void)".
Write a C wrapper "int get_signgam(void) { return signgam; }" and import that.
Or alternatively, foreign import the address of the int and read it directly with 'peek'.
import Foreign ... foreign import ccall "math.h &signgam" signgamC :: Ptr Int32 ... gammaIO :: Double -> IO Double gammaIO x = do lg <- lgammaC x s <- peek signgamC return $ fromIntegral s * exp lg
One potential drawback with that approach is that an implementation
might decide to add thread-safety, in the same manner as glibc does
with errno:
# if !defined _LIBC || defined _LIBC_REENTRANT
/* When using threads, errno is a per-thread value. */
# define errno (*__errno_location ())
# endif
[where __errno_location() returns a thread-specific location via
pthread_getspecific().]
OTOH, a C wrapper will cope with whatever contortions the libc
developers decide to use.
--
Glynn Clements