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−-*- mode: outline; coding: utf-8 -*-
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−
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−* What is BNF?
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−
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−BNF is an acronym for "Backus Naur Form". John Backus and Peter Naur
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−introduced for the first time a formal notation to describe the syntax of a
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−given language (ALGOL 60 programming language).
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−
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−  rfc2234
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−
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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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−  ::=
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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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−  " "
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−    terminals are enclosed in to distinguish them from meta-symbols.
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−
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−* BNF in BNF.
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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 } """