Grammar transformations for optimizing backtrack parsers

We present two grammar transformations which can decrease the search space of generated top-down backtrack parsers. The transformations are simple and can be of practical use.

The first transformation, which is a combination of substitution and left-factorization, is based on the LR-table construction. The second transformation uses the calculation of the sets FIRST and FOLLOW, and a grammar property, called rrelative unambiguity.

The time complexity of the transformations is worst case polynomial and in practical cases linear in the size of the grammar.