BNF syntax.
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/bnf.rst Mon Jun 14 21:11:02 2010 +0300
@@ -0,0 +1,40 @@
+-*- mode: outline; coding: utf-8 -*-
+
+* What is BNF?
+
+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).
+
+ rfc2234
+
+* 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.
+ " "
+ terminals are enclosed in to distinguish them from meta-symbols.
+
+* BNF in BNF.
+
+ 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 } """