Using function headers

When generating C (using the `-fvia-C' directive), one can assist the C compiler in detecting type errors by using the `-#include' directive to provide `.h' files containing function headers.

For example,

typedef unsigned long *StgMallocPtr;
typedef long StgInt;

extern void          initialiseEFS PROTO( (StgInt size) );
extern StgInt        terminateEFS ();
extern StgMallocPtr  emptyEFS();
extern StgMallocPtr  updateEFS PROTO( (StgMallocPtr a, StgInt i, StgInt x) );
extern StgInt        lookupEFS PROTO( (StgMallocPtr a, StgInt i) );

You can find appropriate definitions for `StgInt', `StgMallocPtr', etc using `gcc' on your architecture by consulting `ghc/includes/StgTypes.lh'. The following table summarises the relationship between Haskell types and C types.

C type name              Haskell Type                  
-----------------------------------------------------
`StgChar'       `Char#'              
`StgInt'        `Int#'               
`StgWord'       `Word#'              
`StgAddr'       `Addr#'              
`StgFloat'      `Float#'             
`StgDouble'     `Double#'            
`StgArray'      `Array#'             
`StgByteArray'  `ByteArray#'         
`StgArray'      `MutableArray#'      
`StgByteArray'  `MutableByteArray#'  
`StgStablePtr'  `StablePtr#'         
`StgMallocPtr'  `MallocPtr#'         

Note that this approach is only essential for returning `float's (or if `sizeof(int) != sizeof(int *)' on your architecture) but is a Good Thing for anyone who cares about writing solid code. You're crazy not to do it.