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# BNF grammar parser
# http://en.wikipedia.org/wiki/Backus-Naur_form
require "rsec"
include Rsec::Helpers
def bnf
nbsp = /[\ \t]*/.r
spacee = /\s*/.r # include \n
literal = /".*?"|'.*?'/.r
rule_name = /\<.*?\>/
term = literal | rule_name
list = term.join(nbsp).even
expr = list.join seq(nbsp, '|', nbsp)[1]
rule = seq_ rule_name, '::=', expr
spacee.join(rule).eof
end
require "pp"
pp bnf.parse! DATA.read
__END__
<syntax> ::= <rule> | <rule> <syntax>
<rule> ::= <opt-whitespace> "<" <rule-name> ">" <opt-whitespace> "::=" <opt-whitespace> <expression> <line-end>
<opt-whitespace> ::= " " <opt-whitespace> | ""
<expression> ::= <list> | <list> "|" <expression>
<line-end> ::= <opt-whitespace> <EOL> | <line-end> <line-end>
<list> ::= <term> | <term> <opt-whitespace> <list>
<term> ::= <literal> | "<" <rule-name> ">"
<literal> ::= '"' <text> '"' | "'" <text> "'"
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