Type Inference Verified: Algorithm W in Isabelle/HOL

  • Authors:
  • Wolfgang Naraschewski;Tobias Nipkow

  • Affiliations:
  • Technische Universität München, Institut für Informatik, 80290 München, Germany. e-mail: narasche@in.tum.de;Technische Universität München, Institut für Informatik, 80290 München, Germany. e-mail: nipkow@in.tum.de

  • Venue:
  • Journal of Automated Reasoning
  • Year:
  • 1999

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Abstract

This paper presents the first machine-checked verification of Milner‘s type inference algorithm W for computing the most general type of an untyped λ-term enriched with let-expressions. This term language is the core of most typed functional programming languages and is also known as Mini-ML. We show how to model all the concepts involved, in particular types and type schemes, substitutions, and the thorny issue of “new” variables. Only a few key proofs are discussed in detail. The theories and proofs are developed in Isabelle/HOL, the HOL instantiation of the generic theorem prover Isabelle.