I propose a novel language feature, intensional continuation equality, useful in languages with or without first-class continuations, and show how it enables truly remarkable gains in efficiency of ordinary user programs. Continuations, expressing ``what the program will do from now on,'' are a much-used tool of semantics, and sometimes show up as a user-accessible programming feature. But most use of continuations is parametric, in the sense that functions behave the same way independent of their continuation. I will show that nonparametric use of continuations allows very substantial, almost incredible gains in program speed. Furthermore, this technique is compatible with almost any style of programming language; imperative, functional, even object-oriented.

This technical report has been published as

Intensional Equality ;=) for Continuations. Andrew W. Appel, ACM SIGPLAN Notices 31(2), pp. 55-57, February 1996.