The simplest way to use a simple C function
double fooC( FILE *in, char c, int i, double d, unsigned int u )is to provide a Haskell wrapper:
fooH :: Char -> Int -> Double -> Word -> IO Double
fooH c i d w = _ccall_ fooC ("stdin"::Addr) c i d w
The function `fooH' will unbox all of its arguments, call the C
function `fooC' and box the corresponding arguments.
One of the annoyances about `_ccall_'s is when the C types don't quite match the Haskell compiler's ideas. For this, the `_casm_' variant may be just the ticket (NB: no chance of such code going through a native-code generator):
oldGetEnv name
= _casm_ "%r = getenv((char *) %0);" name >>= \ litstring@(A# str#) ->
return (
if (litstring == "NULL") then
Left ("Fail:oldGetEnv:"++name)
else
Right (unpackCString# str#)
)
The first literal-literal argument to a `_casm_' is like a `printf' format: `%r' is replaced with the "result," `%0'--`%n-1' are replaced with the 1st--nth arguments. As you can see above, it is an easy way to do simple C casting. Everything said about `_ccall_' goes for `_casm_' as well.