Eta - Expansion Does The Trick ( Revised


Partial-evaluation folklore has it that massaging one's source programs can make them specialize better. In Jones, Gomard, and Sestoft's recent textbook, a whole chapter is dedicated to listing such \binding-time improvements": nonstandard use of continuation-passing style, eta-expansion, and a popular transformation called \The Trick". We provide a uniied view of these binding-time improvements, from a typing perspective. Just as a proper treatment of product values in partial evaluation requires partially static values, a proper treatment of disjoint sums requires moving static contexts across dynamic case expressions. This requirement precisely accounts for the nonstandard use of continuation-passing style encountered in partial evaluation. Eta-expansion thus acts as a uniform binding-time coercion between values and contexts, be they of function type, product type, or disjoint-sum type. For the latter case, it enables \The Trick". In this article, we extend Gomard and Jones's partial evaluator for the-calculus,-Mix, with products and disjoint sums; we point out how eta-expansion for ((nite) disjoint sums enables The Trick; we generalize our earlier work by identifying that eta-expansion can be obtained in the binding-time analysis simply by adding two coercion rules; and we specify and prove the correctness of our extension to-Mix.

Cite this paper

@inproceedings{Danvy1996EtaE, title={Eta - Expansion Does The Trick ( Revised}, author={Olivier Danvy and Karoline Malmkj{\ae}r and Jens Palsberg and Karoline Malmkj}, year={1996} }