A Generalization of Dijkstra's Calculus to Typed Program Specifications

  • Authors:
  • Klaus-Dieter Schewe;Bernhard Thalheim

  • Affiliations:
  • -;-

  • Venue:
  • FCT '99 Proceedings of the 12th International Symposium on Fundamentals of Computation Theory
  • Year:
  • 1999

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Abstract

Dijkstra's predicate transformer calculus in its extended form gives an axiomatic semantics to program specifications including partiality and recursion. However, even the classical theory is based on infinitary first order logic which is needed to guarantee the existence of predicate transformers for weakest (liberal) preconditions. This theory can be generalized to higher-order intuitionistic logic. Such logics can be interpreted in topoi. Then each topos E canonically corresponds to a definitionally complete theory T such that E is equivalent to the topos IE(T) of definable types over T. Furthermore, each model of T in an arbitrary topos F canonically corresponds to a logical morphism IE(T) → F. This correspondence enables the definition of a type specification discipline with a semantics based on topoi such that the predicate transformers in the associated logic give an axiomatic semantics for typed program specifications.