Stream fusion: from lists to streams to nothing at all

  • Authors:

  • Duncan Coutts;Roman Leshchinskiy;Don Stewart

  • Affiliations:

  • Oxford University, Oxford, United Kingdom;University of New South Wales, Sydney, Australia;University of New South Wales, Sydney, Australia

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

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Abstract

This paper presents an automatic deforestation system, stream fusion, based on equational transformations, that fuses a wider range of functions than existing short-cut fusion systems. In particular, stream fusion is able to fuse zips, left folds and functions over nested lists, including list comprehensions. A distinguishing feature of the framework is its simplicity: by transforming list functions to expose their structure, intermediate values are eliminated by general purpose compiler optimisations. We have reimplemented the Haskell standard List library on top of our framework, providing stream fusion for Haskell lists. By allowing a wider range of functions to fuse, we see an increase in the number of occurrences of fusion in typical Haskell programs. We present benchmarks documenting time and space improvements.