Automatic online partial evaluation

Abstract

We have solved the problem of constructing a fully automatic online program specializer for an untyped functional language (specifically, the functional subset of Scheme). We designed our specializer, called Fuse, as an interpreter that returns a trace of suspended computations. The trace is represented as a graph, rather than as program text, and each suspended computation indicates the type of its result. A separate process translates the graph into a particular programming language. Producing graphs rather than program text solves problems with code duplication and premature reduce/residualize decisions. Fuse's termination strategy, which employs online generalization, specializes conditional recursive function calls, and unfolds all other calls. This strategy is shown to be both powerful and safe.