The Virtues of Eta-expansion

C Barry Jay and Neil Ghani

Abstract: Interpreting eta-conversion as an expansion rule in the simply-typed lambda-calculus maintains the confluence of reduction in a richer type structure. This use of expansions is supported by categorical models of reduction, where beta-contraction, as the local counit, and eta-expansion, as the local unit, are linked by local triangle laws. The latter form reduction loops, but strong normalisation (to the long beta-eta-normal forms) can be recovered by ``cutting'' the loops.

This paper will be published in the Journal of Functional Programming.

LFCS report ECS-LFCS-92-243, October 1992.

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