Migratory typing: Ten years later

Sam Tobin-Hochstadt, Matthias Felleisen, Robert Findler, Matthew Flatt, Ben Greenman, Andrew M. Kent, Vincent St Amour, T. Stephen Strickland, Asumu Takikawa

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

17 Scopus citations


In this day and age, many developers work on large, untyped code repositories. Even if they are the creators of the code, they notice that they have to figure out the equivalent of method signatures every time they work on old code. This step is time consuming and error prone. Ten years ago, the two lead authors outlined a linguistic solution to this problem. Specifically they proposed the creation of typed twins for untyped programming languages so that developers could migrate scripts from the untyped world to a typed one in an incremental manner. Their programmatic paper also spelled out three guiding design principles concerning the acceptance of grown idioms, the soundness of mixed-typed programs, and the units of migration. This paper revisits this idea of a migratory type system as implemented for Racket. It explains how the design principles have been used to produce the Typed Racket twin and presents an assessment of the project's status, highlighting successes and failures.

Original languageEnglish (US)
Title of host publication2nd Summit on Advances in Programming Languages, SNAPL 2017
EditorsRastislav Bodik, Benjamin S. Lerner, Shriram Krishnamurthi
PublisherSchloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing
ISBN (Electronic)9783959770323
StatePublished - May 1 2017
Event2nd Summit on Advances in Programming Languages, SNAPL 2017 - Asilomar, United States
Duration: May 7 2017May 10 2017

Publication series

NameLeibniz International Proceedings in Informatics, LIPIcs
ISSN (Print)1868-8969


Other2nd Summit on Advances in Programming Languages, SNAPL 2017
Country/TerritoryUnited States


  • Design principles
  • Gradual typing
  • Type systems

ASJC Scopus subject areas

  • Software


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