Pruning in Logic Programming

The logic programming community has a love{hate relationship with operators for pruning the search space of logic programs such as cut, commit, once, conditionals and variations on these. Pruning operators typically are not declarative, result in incom-pleteness and/or unsoundness, decrease readability and exibility of code and make program analysis and transformation more diicult. Despite this, nearly all non-trivial Prolog programs contain cuts, nearly all more recent logic programming languages have similar pruning operators and many languages insist on pruning operators in every clause. In practice, logic programming is less logical than functional programming. Why it this so? Do we really need pruning operators? Can we have suuciently powerful pruning operators which do not destroy the declarative semantics of programs? How are pruning operators related to logic, modes, functions and lazy evaluation? This paper attempts to answer some of these questions.

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