peg.scroll

import ../code/conceptPage.scroll

id peg
name PEG
appeared 2002
tags grammarLanguage
standsFor parsing expression grammar

clocExtensions peg
fileType text
centralPackageRepositoryCount 0

pygmentsHighlighter PEG
 filename grammar_notation.py
 fileExtensions peg
example
 Expr    ← Sum
 Sum     ← Product (('+' / '-') Product)*
 Product ← Value (('*' / '/') Value)*
 Value   ← [0-9]+ / '(' Expr ')'

hasLineComments true
hasComments true

wikipedia https://en.wikipedia.org/wiki/Parsing_expression_grammar
 example
  Value   ← [0-9.]+ / '(' Expr ')'
  Product ← Expr (('*' / '/') Expr)*
  Sum     ← Expr (('+' / '-') Expr)*
  Expr    ← Product / Sum / Value
 related regex
 summary In computer science, a parsing expression grammar, or PEG, is a type of analytic formal grammar, i.e. it describes a formal language in terms of a set of rules for recognizing strings in the language. The formalism was introduced by Bryan Ford in 2004 and is closely related to the family of top-down parsing languages introduced in the early 1970s. Syntactically, PEGs also look similar to context-free grammars (CFGs), but they have a different interpretation: the choice operator selects the first match in PEG, while it is ambiguous in CFG. This is closer to how string recognition tends to be done in practice, e.g. by a recursive descent parser. Unlike CFGs, PEGs cannot be ambiguous; if a string parses, it has exactly one valid parse tree. It is conjectured that there exist context-free languages that cannot be recognized by a PEG, but this is not yet proven. PEGs are well-suited to parsing computer languages (and artificial human languages such as Lojban), but not natural languages where the performance of PEG algorithms is comparable to general CFG algorithms such as the Earley algorithm.
 pageId 892899
 created 2004
 backlinksCount 121
 revisionCount 443
 dailyPageViews 187
 appeared 2002

isbndb 0