Compiling with continuations, continued

  • Authors:
  • Andrew Kennedy

  • Affiliations:
  • Microsoft Research, Cambridge, United Kingdom

  • Venue:
  • ICFP '07 Proceedings of the 12th ACM SIGPLAN international conference on Functional programming
  • Year:
  • 2007

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Abstract

We present a series of CPS-based intermediate languages suitable for functional language compilation, arguing that they have practical benefits over direct-style languages based on A-normal form (ANF) or monads. Inlining of functions demonstrates the benefits most clearly: in ANF-based languages, inlining involves a re-normalization step that rearranges let expressions and possibly introduces a new 'join point' function, and in monadic languages, commuting conversions must be applied; in contrast, inlining in our CPS language is a simple substitution of variables for variables. We present a contification transformation implemented by simple rewrites on the intermediate language. Exceptions are modelled using so-called 'double-barrelled' CPS. Subtyping on exception constructors then gives a very straightforward effect analysis for exceptions. We also show how a graph-based representation of CPS terms can be implemented extremely efficiently, with linear-time term simplification.