Top-to-bottom Parsing Rehabilitated? This note is concerned with the efficiency of the Top-to-Bottom parsing algorithm as used in connection with programming language grammars. It is shown, for instance, that retracing of unprofitable paths can often be eliminated by a suitable rearrangement of the productions defining the grammar. The essential weakness of the method is in dealing with complicated syntactic structures which are in practice only sparsely occupied, e.g., arithmetic expressions. CACM April, 1967 Brooker, R. A. CA670403 JB February 28, 1978 11:32 AM 1612 4 1612 1781 4 1612 1945 4 1612 1139 5 1612 1612 5 1612 1612 5 1612 1612 5 1612