Shallow Backtracking in Prolog Programs

The efficiency of Prolog compilers is increasing rapidly but the Prolog programs still cannot compete with traditional languages when executing simple conditionals. In this paper we present a possibility to increase Prolog performance by exploiting the shallow backtracking. Shallow backtracking is initiated when a call fails to unify with the head of a clause and it backtracks to another clause in the same procedure, as opposed to deep backtracking which requires going back in the search tree and trying an alternative of a previous goal. We introduce modified OR-level instructions and data management and discuss the impact on performance of Prolog programs.