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In formal language theory, a context-free grammar ( CFG) is a formal grammar whose production rules can be applied to a nonterminal symbol regardless of its context. In particular, in a context-free grammar, each production rule is of the form. with a single nonterminal symbol, and a string of terminals and/or nonterminals ( can be empty).
Abstract syntax tree of the arithmetic expression "a^2+4*b" wrt. the example grammar (top) and its Chomsky normal form (bottom) The following grammar, with start symbol Expr , describes a simplified version of the set of all syntactical valid arithmetic expressions in programming languages like C or Algol60 .
In formal language theory, a context-free grammar is in Greibach normal form ( GNF) if the right-hand sides of all production rules start with a terminal symbol, optionally followed by some variables. A non-strict form allows one exception to this format restriction for allowing the empty word (epsilon, ε) to be a member of the described language.
The set of all context-free languages is identical to the set of languages accepted by pushdown automata, which makes these languages amenable to parsing.Further, for a given CFG, there is a direct way to produce a pushdown automaton for the grammar (and thereby the corresponding language), though going the other way (producing a grammar given an automaton) is not as direct.
English grammar is the set of structural rules of the English language.This includes the structure of words, phrases, clauses, sentences, and whole texts.. This article describes a generalized, present-day Standard English – a form of speech and writing used in public discourse, including broadcasting, education, entertainment, government, and news, over a range of registers, from formal to ...
Linguistic prescription[ a] is the establishment of rules defining preferred usage of language. [ 1][ 2] These rules may address such linguistic aspects as spelling, pronunciation, vocabulary, morphology, syntax, and semantics. Sometimes informed by linguistic purism, [ 3] such normative practices often propagate the belief that some usages are ...
Syntax was recognized as the focal point of language production, in which a finite set of rules can produce an infinite number of sentences. Subsequently, morphology (i.e. the study of structure and formation of words) and phonology (i.e. the study of organization of sounds in languages) were relegated in importance.
In linguistics, a grammar is the set of rules for how a natural language is structured, as demonstrated by its speakers or writers. Grammar rules may concern the use of clauses, phrases, and words. The term may also refer to the study of such rules, a subject that includes phonology, morphology, and syntax, together with phonetics, semantics ...