bnf.rst
author Oleksandr Gavenko <gavenkoa@gmail.com>
Mon, 30 Jan 2017 00:44:30 +0200
changeset 2075 ccaa2f364422
parent 1912 8b81a8f0f692
child 2228 837f1337c59b
permissions -rw-r--r--
Improve page formatting.
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.. -*- coding: utf-8; -*-
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=====
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 BNF
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=====
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What is BNF?
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============
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.. contents::
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   :local:
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BNF is an acronym for "Backus Naur Form". John Backus and Peter Naur introduced
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for the first time a formal notation to describe the syntax of a given language
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(ALGOL 60 programming language).
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See: :rfc:`2234`.
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BNF syntax
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==========
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The meta-symbols of BNF are:
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  ``::=``
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    Meaning "is defined as".
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  ``|``
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    Meaning "or".
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  ``<``,  ``>``
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    Angle brackets used to surround category names (some times skipped).
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  ``[``,  ``]``
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    Optional items are enclosed in.
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  ``{``,  ``}``
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    Repetitive items (zero or more times) are enclosed in.
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  ``"abc..."``
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    Terminals are enclosed in to distinguish them from meta-symbols.
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BNF in BNF
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==========
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::
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  syntax     ::=  { rule }
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  rule       ::=  identifier  "::="  expression
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  expression ::=  term { "|" term }
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  term       ::=  factor { factor }
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  factor     ::=  identifier |
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                  quoted_symbol |
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                  "("  expression  ")" |
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                  "["  expression  "]" |
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                  "{"  expression  "}"
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  identifier ::=  letter { letter | digit }
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  quoted_symbol ::= """ { any_character } """
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