Blame for all

Amal Ahmed, Robert Bruce Findler, Jeremy G. Siek, Philip Wadler

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract / Description of output

Several programming languages are beginning to integrate static and dynamic typing, including Racket (formerly PLT Scheme), Perl 6, and C# 4.0 and the research languages Sage (Gronski, Knowles, Tomb, Freund, and Flanagan, 2006) and Thorn (Wrigstad, Eugster, Field, Nystrom, and Vitek, 2009). However, an important open question remains, which is how to add parametric polymorphism to languages that combine static and dynamic typing. We present a system that permits a value of dynamic type to be cast to a polymorphic type and vice versa, with relational parametricity enforced by a kind of dynamic sealing along the lines proposed by Matthews and Ahmed (2008) and Neis, Dreyer, and Rossberg (2009). Our system includes a notion of blame, which allows us to show that when casting between a more-precise type and a less-precise type, any cast failures are due to the less-precisely-typed portion of the program. We also show that a cast from a subtype to its supertype cannot fail.
Original languageEnglish
Title of host publicationProceedings of the 38th annual ACM SIGPLAN-SIGACT symposium on Principles of Programming Languages (POPL '11)
Place of PublicationNew York, NY, USA
Number of pages14
ISBN (Print)978-1-4503-0490-0
Publication statusPublished - 2011

Keywords / Materials (for Non-textual outputs)

  • blame tracking
  • casts
  • coercions
  • lambda-calculus


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