Editing Backus–Naur form (section)

== Impact ==
BNF significantly influenced programming language development, notably as the basis for early [[compiler-compiler]] systems. Examples include Edgar T. Irons' "A Syntax Directed Compiler for ALGOL 60" and Brooker and Morris' "A Compiler Building System," which directly utilized BNF.<ref>{{cite book |last1=McKeeman |first1=W. M. |title=A Compiler Generator |last2=Horning |first2=J.J. |last3=Wortman |first3=D. B. |publisher=Prentice-Hall |year=1970 |isbn=978-0-13-155077-3}}</ref> Others, like Schorre's [[META II]], adapted BNF into a programming language, replacing <code>&lt; &gt;</code> with quoted strings and adding operators like $ for repetition, as in:<syntaxhighlight lang="ebnf"> EXPR = TERM $('+' TERM .OUT('ADD') | '-' TERM .OUT('SUB')); </syntaxhighlight>This influenced tools like [[yacc]], a widely used [[parser generator]] rooted in BNF principles, and Unix utilities like [[yacc]].<ref>{{Citation |title=Source forge |type=project |url=http://bnfparser2.sourceforge.net/ |contribution=BNF parser²}}</ref> BNF remains one of the oldest computer-related notations still referenced today, though its variants often dominate modern applications.

Examples of its use as a metalanguage include defining arithmetic expressions:<syntaxhighlight lang="bnf"> <expr> ::= <term> | <expr> <addop> <term> </syntaxhighlight>Here, {{Code|1=<expr>|2=bnf}} can recursively include itself, allowing repeated additions.
BNF today is one of the oldest computer-related languages still in use.{{citation needed|date=March 2020}}