| slovo | definícia |
cfg
(foldoc) | context-free grammar
CFG
(CFG) A grammar where the syntax of each constituent
(syntactic category or terminal symbol) is independent of the
symbols occuring before and after it in a sentence. A
context-free grammar describes a context-free language.
Context-free grammars can be expressed by a set of "production
rules" or syntactic rules. For example, a language with symbols
"a" and "b" that must occur in unequal numbers can be represented
by the CFG:
S → U | V
U → TaU | TaT | UaT
V → TbV | TbT | VbT
T → aTbT | bTaT | ε
meaning the top-level category "S" consists of either a "U" or a
"V" and so on. The special category "ε" represents the empty
string. This grammar is context-free because each rule has a
single symbol on its left-hand side.
Parsers for context-free grammars are simpler than those for
context-dependent grammars because the parser need only know the
current symbol.
Algol was (one of?) the first languages whose syntax was
described by a context-free grammar. This became a common
practice for programming languages and led to the notation for
grammars called Backus-Naur Form.
(2014-11-24)
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