Proof tool support for explicit strictness

  • Authors:

  • Marko van Eekelen;Maarten de Mol

  • Affiliations:

  • Institute for Computing and Information Sciences, Radboud University Nijmegen, The Netherlands;Institute for Computing and Information Sciences, Radboud University Nijmegen, The Netherlands

  • Venue:
  • IFL'05 Proceedings of the 17th international conference on Implementation and Application of Functional Languages
  • Year:
  • 2005

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Abstract

In programs written in lazy functional languages such as for example Clean and Haskell, the programmer can choose freely whether particular subexpressions will be evaluated lazily (the default) or strictly (must be specified explicitly). It is widely known that this choice affects resource consumption, termination and semantics in several ways. However, functional programmers tend to be less aware of the consequences for logical program properties and formal reasoning. This paper aims to give a better understanding of the concept of explicit strictness and its impact on properties and reasoning. It will be shown that explicit strictness may make reasoning more cumbersome, due to the introduction of additional definedness conditions. Fortunately, these definedness conditions can be handled quite effectively by proof assistants. This paper describes the specific support that is offered by Sparkle for expressing and proving definedness conditions. This support makes reasoning with explicit strictness almost appear like reasoning without explicit strictness. To our knowledge, Sparkle is currently the only proof assistant with such strictness specific support.