Abstract

. We present two optimizations for making Mercury programs tail recursive. Both operate by taking computations that occur after a recursive call and moving them before the recursive call, modifying them as necessary. The rst optimization moves calls to associative predicates; it is a pure source to source transformation. The second optimization moves construction unications; it required extensions to the mode system (to record aliases) and to the parameter passing convention (to allow arguments to be returned in memory). The two optimizations are designed to work together, and can make a large class of programs tail recursive. 1 Introduction Recursive calls are often very close to being the last action in a clause. Frequently, however, the recursive call computes a value which must be put into a memory cell or used in a simple computation. Since the Mercury execution algorithm [13] requires both of these kinds of actions to be performed after the call, such clauses are not ...

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