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一个Pascal语言分析器

   EBNF = { Production } .

   Production = nonterminal "=" Expression "." .

   Expression = Term { "|" Term } .

   Term = Factor { Factor } .

   Factor = nonterminal
            | terminal
            | "[" Expression "]"
            | "(" Expression ")"
            | "{" Expression "}" .

    nonterminal = letter {letter | lowline | digit} .

    terminal =  "'" noquote1 {noquote1} "'" | '"' noquote2 {noquote2} '"' .