Getting constants from #defines
simonmar at microsoft.com
Wed Jun 26 09:20:52 EDT 2002
> I was expecting something like
> foreign import ccall unsafe "static ncurses.h ERR" cERR :: CInt
> to allow me to access the value of ERR (a #define) as cERR.
> However, as
> far as I can tell GHC is trying to compile this as if ERR was a
> function. This seems silly to me as a function can always be defined
> with a type "a -> b" where "a", "b" or both can be "()" so this should
> be unambiguous.
The FFI doesn't have support for grabbing the values of #defines - you need to use another tool to do this (autoconf, hsc2hs, c2hs, green-card, hdirect, whatever).
The declaration above binds cERR to a function of zero arguments. i.e. in C-speak this would be
void cERR( void );
A function of type a->b has one argument of type 'a', not zero.
More information about the FFI