Relating typability and expressiveness in finite-rank intersection type systems

摘要

We investigate finite-rank intersection tyep systems,analyzing the complexity of their tyep inference prolbems and their relation to the problem of recognizing semantically equavalent terms.Intersection types allow something of type T_1^T_2 to be used in some places tt type T_1 and in other palces at type T_2.A finite-rank intersection type system bounds how deeply the ^ can appear in type expressions.Such type systems enjoy strong normalization,subject rduiton,and omputable tyep inferene,ad they suport a pragmatics for implementating parametric plymorphism.As a consequence,they provide a ocnceptaually simple and tractable alternative to the impredicative polymorphism of System F and its extensions,while typing many more programs than the Hidley-Miliner tyep system found in ML and Haskell.