Space-efficient gradual typing

Abstract

Gradual type systems offer a smooth continuum between static and dynamic typing by permitting the free mixture of typed and untyped code. The runtime systems for these languages, and other languages with hybrid type checking, typically enforce function types by dynamically generating function proxies. This approach can result in unbounded growth in the number of proxies, however, which drastically impacts space efficiency and destroys tail recursion.

We present a semantics for gradual typing that is based on coercions instead of function proxies, and which combines adjacent coercions at runtime to limit their space consumption. We prove bounds on the space consumed by coercions as well as soundness of the type system, demonstrating that programmers can safely mix typing disciplines without incurring unreasonable overheads. Our approach also detects certain errors earlier than prior work.

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Correspondence to David Herman.

Additional information

David Herman was supported by a grant from the Mozilla Corporation. Cormac Flanagan was supported by a Sloan Fellowship and by NSF grant CCS-0341179. Aaron Tomb was also supported by NSF grant CCS-0341179. For Herman, most of this work was done at Northeastern University, Boston, MA.

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Herman, D., Tomb, A. & Flanagan, C. Space-efficient gradual typing. Higher-Order Symb Comput 23, 167 (2010). https://doi.org/10.1007/s10990-011-9066-z

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Keywords

  • Gradual typing
  • Coercions
  • Casts
  • Type dynamic