On the Parsing of Deterministic Languages
Journal of the ACM (JACM)
Deterministic parsing of ambiguous grammars
Communications of the ACM
Revised report on the algorithm language ALGOL 60
Communications of the ACM
Report on the algorithmic language ALGOL 60
Communications of the ACM
PASCAL user manual and report
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The classical pumping lemma [BP&S] and Ogden's lemma [Og] are among the most powerful tools we possess for proving that languages are not context-free. Hence one goal of recent research has been to obtain analogous theorems for subclasses of the context-free languages. We establish here a property of LL(k) derivation trees which is analogous to the left part property for strict deterministic grammars[H&H]. We show that our property characterizes LL(k) grammars and use it to establish two iteration theorems for the LL languages. These theorems, in turn, enable us to prove simply and rigorously that a variety of LR languages are not LL. In particular, the “dangling” Algol 60 IF-THEN-ELSE construct allowed in Pascal and PL/1 cannot be generated by an LL(k) grammar.