Traditional techniques for implementing polymorphism use a universal representation for objects of unknown type. Often, this forces a compiler to use universal representations even if the types of objects are known. We examine an alternative approach for compiling polymorphism where types are passed as arguments to polymorphic routines in order to determine the representation of an object. This approach allows monomorphic code to use natural, e cient representations, supports separate compilation of polymorphic de nitions and, unlike coercion-based implementations of polymorphism, natural representations can be used for mutable objects such as refs and arrays. We are particularly interested in the typing properties of an intermediate language that allows run-time type analysis to be coded within the language. This allows us to compile many representation transformations and many language features without adding new primitive operations to the language. In this paper, we provide a core...
Robert Harper, J. Gregory Morrisett