Backus-Naur Form

The so-called Backus-Naur Form (or short BNF) was initially used for the report of the Algol-60 programming language. In BNF all production rules are of the form

< A > ---> alpha

where < A > is a nonterminal and alpha an arbitrary sequence of terminals and nonterminals.

If several production rules share the left hand side

< A > ---> alpha

< A > --->

it is permitted to join them into one rule:

< A > ---> alpha |

epsilon or <empty> is used to specify the empty sequence.

BNF comes in various forms. At times ::= or = is used instead of --->.