2014/05/22 by Mikhail Barash, Alexander Okhotin
Computer Science · #cs.FL
paper · pdf · doi:10.4204/eptcs.151.6
published as EPTCS 151, 2014, pp. 94-108 · In Proceedings AFL 2014, arXiv:1405.5272
arxiv created 2014/05/22 · arxiv updated 2014/05/23
In a recent paper (M. Barash, A. Okhotin, "Defining contexts in context-free grammars", LATA 2012), the authors introduced an extension of the context-free grammars equipped with an operator for referring to the left context of the substring being defined. This paper proposes a more general model, in which context specifications may be two-sided, that is, both the left and the right contexts can be specified by the corresponding operators. The paper gives the definitions and establishes the basic theory of such grammars, leading to a normal form and a parsing algorithm working in time O(n4), where n is the length of the input string.