[MLton-user] opaque types and ffi

[Vesa A Norrman]

> Taking the idea a bit further, perhaps it would be nice to have the type
> be 'a pointer, with FFI allowed for any 'a. This would allow the
> programmer to create any number of distinct pointer types with "phantom"
> arguments (if I recall correctly this idiom is used all over in mlton
> itself). This might be a way to do what Vesa wants.

What I was thinking was probably something like:

structure Voidp :> VOIDP
  where type t may pass through ffi
= struct
    type t = Word32.word
    ...
  end

Obviously this is not possible...

About practical matters, I did not know about MLton.pointer.
Is an ffi call required for testing for null pointer? Vesa