Intersection types for unbind and rebind

Mariangiola Dezani-Ciancaglini
Paola Giannini
Elena Zucca

We define a type system with intersection types for an extension of lambda-calculus with unbind and rebind operators. In this calculus, a term with free variables, representing open code, can be packed into an "unbound" term, and passed around as a value. In order to execute inside code, an unbound term should be explicitly rebound at the point where it is used. Unbinding and rebinding are hierarchical, that is, the term can contain arbitrarily nested unbound terms, whose inside code can only be executed after a sequence of rebinds has been applied. Correspondingly, types are decorated with levels, and a term has type decorated with k if it needs k rebinds in order to reduce to a value. With intersection types we model the fact that a term can be used differently in contexts providing different numbers of unbinds. In particular, top-level terms, that is, terms not requiring unbinds to reduce to values, should have a value type, that is, an intersection type where at least one element has level 0. With the proposed intersection type system we get soundness under the call-by-value strategy, an issue which was not resolved by previous type systems.

In Elaine Pimentel, Betti Venneri and Joe Wells: Proceedings Fifth Workshop on Intersection Types and Related Systems (ITRS 2010), Edinburgh, U.K., 9th July 2010, Electronic Proceedings in Theoretical Computer Science 45, pp. 45–58.
Published: 21st January 2011.

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