Multi-return function call

Abstract

It is possible to extend the basic notion of “function call” to allow functions to have multiple return points. This turns out to be a surprisingly useful mechanism. This article conducts a fairly wide-ranging tour of such a feature: a formal semantics for a minimal $\lambda$ -calculus capturing the mechanism; motivating examples; monomorphic and parametrically polymorphic static type systems; useful transformations; implementation concerns and experience with an implementation; and comparison to related mechanisms, such as exceptions, sum-types and explicit continuations. We conclude that multiple-return function call is not only a useful and expressive mechanism, at both the source-code and intermediate-representation levels, but also quite inexpensive to implement.