Controlled Grammatic

A new approach to ambiguity of context-free grammars is presented, and within this approach the LL and LR techniques are generalized to solve the following problems for large classes of ambiguous grammars: |Construction of a parser that accepts all sentences generated by the grammar, and which always terminates in linear time. |Identiication of the structural ambiguity: a nite set of pairs of partial parse trees is constructed; if for each pair the two partial parse trees are semantically equivalent, the ambiguity of the grammar is semantically irrelevant. The user may control the parser generation so as to get a parser which nds some speciic parse trees for the sentences. The generalized LL and LR techniques will still guarantee that the resulting parser accepts all sentences and terminates in linear time on all input. 1. INTRODUCTION For unambiguous grammars we have the powerful LL and LR techniques that for large classes can verify their unambiguity and construct complete linear time parsers, i.e. parsers that accept the full languages and terminate in linear time on all inputs. With a new approach to ambiguity we generalize the LL and LR techniques to deal with large classes of ambiguous grammars as well; thus characterizing the ambiguity and constructing complete linear time parsers.