контекстно-свободная грамматика
контекстно-свободная (бесконтекстная) грамматика
(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. Parsers for context-free grammars are simpler than those for context-dependent grammars because the parser need only know the current symbol. Algol was 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.