Computers

A Wikipedia article that defines context free grammars and uses them to generate context free languages.

An article defining the grammar and how Binary Normal Form (BNF) is used to parse words in a context free language. An example shows how operator precedence is preserved in a context free grammar.

A survey article on formal systems that define families of formal languages arising in many computer science applications with primary focus on context-free languages.

Lecture notes defining context free grammars and closure and decidability properties of context free languages. There is a short section showing that natural languages are not context free.