There and back again functional pearl

Olivier Danvy, Mayer Goldberg

Research output: Contribution to conferencePaperpeer-review

5 Scopus citations


We present a programming pattern where a recursive function traverses a data structure-typically a list-at return time. The idea is that the recursive calls get us there (typically to a base case) and the returns get us back again while traversing the data structure. We name this programming pattern of traversing a data structure at return time "There And Back Again" (TABA). The TABA pattern directly applies to computing a symbolic convolution. It also synergizes well with other programming patterns, e.g., dynamic programming and traversing a list at double speed. We illustrate TABA and dynamic programming with Catalan numbers. We illustrate TABA and traversing a list at double speed with palindromes and we obtain a novel solution to this traditional exercise. A TABA-based function written in direct style makes full use of an Algol-like control stack and needs no heap allocation. Conversely, in a TABA-based function written in continuation-passing style, the continuation acts as a list iterator. In general, the TABA pattern saves one from constructing intermediate lists in reverse order.

Original languageEnglish
Number of pages5
StatePublished - 1 Dec 2002
EventProceedings of the Seventh ACM SIGPLAN; International Conference on Functional Programming (ICFP'02) - Pittsburgh, PA, United States
Duration: 4 Oct 20026 Oct 2002


ConferenceProceedings of the Seventh ACM SIGPLAN; International Conference on Functional Programming (ICFP'02)
Country/TerritoryUnited States
CityPittsburgh, PA


  • Catalan numbers
  • Continuation-based programming
  • Palindrome detection
  • Symbolic convolutions

ASJC Scopus subject areas

  • Software


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