What is Your Function? Static Pattern Matching on Function Behavior

We de ne a new notion of function pattern, which supports runtime pattern matching on functions based on their behavior. The ability to runtime dispatch on function type information enables new programmer expressiveness, including support of overloading on higherorder functions as well as other useful patterns. We formally present a type inference system for function patterns. The system answers questions of function pattern matching by recursively invoking the type inference algorithm. The recursive invocation contains some delicate issues of self-referentiality that we address.