Recasting MLF

Abstract : The language MLF has been proposed as an alternative to System F that permits partial type inference a la ML. It differs from System F by its types and type-instance relation. Unfortunately, the definition of type instance is only syntactic, and not underpinned by some underlying semantics. It has so far only been justified a posteriori by the type soundness result. In this work, we revisit MLF following a more progressive approach building on System F. We argue that System F is not a well-suited language for ML-style type inference because it fails to share some closely related typing derivations. We solve this problem in Curry style MLF by enriching types with a new form of quantification that may represent a whole collection of System-F types. This permits a natural interpretation of MLF types as sets of System-F types and defining the instance relation as set containment of the interpretations. We also give an equivalent syntactic definition of the type-instance, presented as a set of inference rules. We derive a Church-style version of MLF by further refining types so as to distinguish between user-provided and inferred type information. We show an embedding of ML in MLF and an encoding of System F into MLF. Besides, as MLF is more expressive than System F, an encoding of MLF is given towards an extension of System F with local binders.
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Submitted on : Wednesday, December 3, 2008 - 2:02:23 PM
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Didier Le Botlan, Didier Rémy. Recasting MLF. Information and Computation, Elsevier, 2009, Volume 207, Issue 6, June 2009, Pages 726-785, 207 (6), pp.726-785. ⟨10.1016/j.ic.2008.12.006⟩. ⟨inria-00156628v4⟩



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