Malloc Pointers and Stable Pointers: Improving Haskell's Foreign Language Interface

The Glasgow Haskell compiler provides a foreign language interface which allows Haskell programs to call arbitrary C functions. This has been used both to implement the standard Haskell IO system and a variety of applications including an arcade game 8], and a graphical user interface to a database 19]. The theoretical problems associated with using impure functions from pure functional languages are avoided through the use of monads 17]; and the mismatch between strict languages with no garbage collection and lazy languages with garbage collection is tackled by unboxing (that is, forcing evaluation of arguments and stripping oo any header information) 15]. Whilst this works well for simple examples, it is unsuitable when one wants to pass arguments (or results) which are lazy, polymorphic or very large. We describe two extensions to the garbage collector which solve these problems by allowing better interaction between the Haskell garbage collector and memory allocation in the imperative world.