Ptr and ForeignPtr Questions
Sun, 23 Sep 2001 19:43:16 -0700
At 2001-09-23 19:14, Manuel M. T. Chakravarty wrote:
>Hmm, we must be misunderstanding each other. Given that you
> foreign import strcat :: Ptr CChar -> Ptr CChar -> IO (Ptr CChar)
>How do you want to know whether the C prototype is
> char *strcat(char *dest, const char *src);
> char *strcat(char *dest, char *src);
I was just hoping for GHC to be able to spit out headers for 'foreign
import' functions that the user could then define. This merely means a
map from some restricted set of Haskell function types to C types.
But it looks like you want to be able to arbitrarily import any C library
function. Of course this means a map from C functions to Haskell
In the case you gave Haskell could get away with calling strcat using
...even if the function had actually been defined like this:
char* strcat(char*,const char*);
This is quite safe from a 'const' point of view. More difficult is this:
const char* foo()
...since the best the FFI can do is this:
foreign import foo :: IO (Ptr CChar)
...which is certainly _not_ const-safe.
Perhaps one could have ConstPtrs, which didn't allow writes, and allow
those in FFI.
At 2001-09-23 19:21, Manuel M. T. Chakravarty wrote:
>If you are writing a Haskell binding to a large C library
>that has hundreds of functions, it is extremely unattractive
>to write "impedance matchers" like `MyModule__StringCopy'
I'm taking an approach similar to JNI, in which the user defines in C
what has been declared in Haskell. But what you want to do is to allow
the user to declare in Haskell what has been defined in C, obviously a
more ambitious goal. Const pointers are not your only worry; how would
you deal with structs?
Ashley Yakeley, Seattle WA