Parsing expression grammar: Difference between revisions

Revision as of 10:36, 19 July 2023

Revision as of 15:50, 25 December 2023

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The consequence is that if a CFG is transliterated directly to a PEG, any ambiguity in the former is resolved by deterministically picking one parse tree from the possible parses. By carefully choosing the order in which the grammar alternatives are specified, a programmer has a great deal of control over which parse tree is selected.

Like [[Boolean grammar|boolean context-free grammars]], parsingParsing expression grammars also add the and- and not- [[syntactic predicate]]s. Because they can use an arbitrarily complex sub-expression to "look ahead" into the input string without actually consuming it, they provide a powerful syntactic [[Parsing#Lookahead|lookahead]] and disambiguation facility, in particular when reordering the alternatives cannot specify the exact parse tree desired.

=== Operational interpretation of parsing expressions ===