Merging Gradual Typing
summary
A new λM⋆ calculus combines gradual typing with an intersection-based merge operator, gives a typed-driven runtime (no separate cast calculus), and formalizes casts and projections mutually. Paper proves type safety and encodes GTFL≲, implements metatheory in Coq (artifacts available), and separates ambiguity errors from type errors using a disjointness criterion. The original DGG fails but a guarded variant holds via a semantic precision relation built as a step-indexed logical relation. Results support first-class classes and dynamic inheritance.
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