At 2001-09-23 19:14, Manuel M. T. Chakravarty wrote:
Hmm, we must be misunderstanding each other. Given that you have
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);
or
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 functions. In the case you gave Haskell could get away with calling strcat using this: char* strcat(char*,char*); ...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() { return "hello"; } ...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' manually.
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