Foreign function binding interface.

The Foreign and Cstubs modules provide concrete implementations.

type 'a fn
type 'a return
val (@->) : 'a typ -> 'b fn -> ('a -> 'b) fn
val returning : 'a typ -> 'a return fn
type 'a result
val foreign : string -> ('a -> 'b) fn -> ('a -> 'b) result
val foreign_value : string -> 'a typ -> 'a ptr result