Corpse reviver: sound and efficient gradual typing via contract verification

Gradually typed programming languages permit the incremental addition of static types to untyped programs. To remain sound, insert run-time checks at boundaries between and code. Unfortunately, performance studies have shown that overhead these can be disastrously high, calling into question viability sound gradual typing. In this paper, we show by building on existing work soft contract verification, reduce or eliminate overhead. Our key insight is while code cannot trusted a type system, there no need consider only worst case when optimizing gradually program. Instead, statically analyze portions program prove almost all dynamic implied fail, eliminated compile time. analysis modular, applied any portion We evaluate approach dozen programs previously prohibitive overhead—with median 2.5× up 80.6× in case—and most cases, suffering 1.5× case.