1 -*- mode: outline; coding: utf-8 -*-

     2 

     3 * What is BNF?

     4 

     5 BNF is an acronym for "Backus Naur Form". John Backus and Peter Naur

     6 introduced for the first time a formal notation to describe the syntax of a

     7 given language (ALGOL 60 programming language).

     8 

     9   rfc2234

    10 

    11 * BNF syntax.

    12 

    13 The meta-symbols of BNF are:

    14 

    15   ::=

    16     meaning "is defined as"

    17   |

    18     meaning "or"

    19   < >

    20     angle brackets used to surround category names (some times skipped).

    21   [  ]

    22     optional items are enclosed in.

    23   { }

    24     repetitive items (zero or more times) are enclosed in.

    25   " "

    26     terminals are enclosed in to distinguish them from meta-symbols.

    27 

    28 * BNF in BNF.

    29 

    30   syntax     ::=  { rule }

    31   rule       ::=  identifier  "::="  expression

    32   expression ::=  term { "|" term }

    33   term       ::=  factor { factor }

    34   factor     ::=  identifier |

    35                   quoted_symbol |

    36                   "("  expression  ")" |

    37                   "["  expression  "]" |

    38                   "{"  expression  "}"

    39   identifier ::=  letter { letter | digit }

    40   quoted_symbol ::= """ { any_character } """