From parametric polymorphism to models of polymorphic FPC

This paper shows how PILLY (Polymorphic Intuitionistic / Linear Lambda calculus with a fixed point combinator Y ) with parametric polymorphism can be used as a metalanguage for domain theory, as originally suggested by Plotkin more than a decade ago. Using Plotkin’s encodings of recursive types in PILLY we show how parametric models of PILLY give rise to models of FPC, a simply typed lambda calculus with recursive types and an operational call-by-value semantics, reflecting a classical result from domain theory. Essentially, this interpretation is an interpretation of intuitionistic logic into linear logic first discovered by Girard, which in this paper is extended to deal with recursive types. Of particular interest is a model based on “admissible” pers over a reflexive domain, the theory of which can be seen as a domain theory for (impredicative) polymorphism. We show how this model gives rise to a parametric and computationally adequate model of PolyFPC, an extension of FPC with impredicative polymorphism. This is to the author’s knowledge the first denotational model of a non-linear language with parametric polymorphism and recursive types.