Profilers play an important role in the development of efficient programs. Profiling techniques developed for traditional languages are inadequate for logic programming languages, for a number of reasons: first, the flow of control in logic programming languages, involving back‐tracking and failure, is significantly more complex than in traditional languages; secondly, the time taken by a unification operation, the principal primitive operation of such languages, cannot be predicted statically because it depends on the size of the input; and finally, programs may change at run‐time because clauses may be added or deleted using primitives such as assert and retract. This paper describes a simple profiler for Prolog. The ideas outlined here may be used either to implement a simple interactive profiler, or integrated into Prolog compilers.
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