Formal languages
An efficient context-free parsing algorithm
Communications of the ACM
Correctness-preserving program transformations
POPL '75 Proceedings of the 2nd ACM SIGACT-SIGPLAN symposium on Principles of programming languages
Context-sensitive immediate constituent analysis—context-free languages revisited
STOC '69 Proceedings of the first annual ACM symposium on Theory of computing
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The method of local constraints attempts to describe context-free languages in an apparently context-sensitive form which helps to retain the intuitive insights about the grammatical structure. This form of description, while apparently context-sensitive is, in fact, context-free and allows a program derivation structure to be represented as a tree with additional constraints, thus allowing for the possibility of a correctness proof in the form of Knuthian semantics. A part of ALGOL 60 syntax has been restated as a grammar with local constraints. It is also shown that parsing of grammars with local constraints can be carried out by a suitable extension of Early's algorithm. Finally, the relationship of local constraints to the semantics of programs is discussed in Section 4 by considering some program transformations.