Using a Continuation Twice and Its Implications for the Expressive Power of call/cc

  • Authors:
  • Hayo Thielecke

  • Affiliations:
  • Department of Computer Science, Queen Mary and Westfield College, University of London. ht@dcs.qmw.ac.uk

  • Venue:
  • Higher-Order and Symbolic Computation
  • Year:
  • 1999

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Abstract

We study the implications for the expressive power of call/ccof upward continuations, specifically the idiom of using a continuation twice. Although such control effects were known to Landin and Reynolds whenthey invented J and {\tt escape}, the forebears of call/cc, they still act as a conceptual pitfall for some attempts to reason about continuations. We use this idiom to refute some recent conjectures about equivalences in a language with continuations, but no other effects. This shows that first-class continuations as given by call/cchave greater expressive power than one would expect from {\tt goto} or exits.