Challenges and progress toward efficient gradual typing (invited talk)

Mixing static and dynamic type checking in the same language is catching on, with the TypeScript and Flow variants of JavaScript, the MyPy and Reticulated variants of Python, the Strongtalk and Gradualtalk variants of Smalltalk, as well as Typed Racket, Typed Clojure, and Perl 6. The gradual typing approach to such mixing seeks to protect the statically typed code from the dynamically typed code, allowing compilers to leverage type information when optimizing the static code. Unfortunately, ensuring soundness requires runtime checking at the boundaries of typed and untyped code, and the cost of this checking can drown out the performance benefits of optimization. For example, in Typed Racket, some partially typed programs are 1000X slower than the untyped or fully typed version of the same program. But all is not lost! In this talk I present the results of ongoing research to tame the runtime overheads of gradual typing in the context of a prototype compiler, named Grift, that we are developing at Indiana University.