Migrating to newer Gradle.
.. -*- coding: utf-8; -*-
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BNF
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What is BNF?
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.. contents::
:local:
BNF is an acronym for "Backus Naur Form". John Backus and Peter Naur introduced
for the first time a formal notation to describe the syntax of a given language
(ALGOL 60 programming language).
See: :rfc:`2234`.
BNF syntax
==========
The meta-symbols of BNF are:
``::=``
Meaning "is defined as".
``|``
Meaning "or".
``<``, ``>``
Angle brackets used to surround category names (some times skipped).
``[``, ``]``
Optional items are enclosed in.
``{``, ``}``
Repetitive items (zero or more times) are enclosed in.
``"abc..."``
Terminals are enclosed in to distinguish them from meta-symbols.
BNF in BNF
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::
syntax ::= { rule }
rule ::= identifier "::=" expression
expression ::= term { "|" term }
term ::= factor { factor }
factor ::= identifier |
quoted_symbol |
"(" expression ")" |
"[" expression "]" |
"{" expression "}"
identifier ::= letter { letter | digit }
quoted_symbol ::= """ { any_character } """