Substring parsing for arbitrary context-free grammars

Abstract

A substring recognizer for a language L determines whether a string s is a substring of a sentence in L , i.e., substring-recognize(s) succeeds if and only if ∃ v, w : vsw ∈ L . The algorithm for substring recognition presented here accepts general context-free grammars and uses the same parse tables as the general context-free parsing algorithm from which it was derived. Substring recognition can be useful for noncorrecting syntax error recovery and for incremental parsing. By extending the substring recognizer with the ability to generate trees for the possible contextual completions of the substring, we obtain a substring parser , which can be used in a syntax-directed editor to complete fragments of sentences.