start = rules:rules { return rules; }

rules = rule+

rule =
  n:number? _ rule:parts {
    return {n:n, rule:rule}
  }

number = "[" n:digits "]" { return n; }

parts = name:symbol _ "::=" _ expression:expression _r? { return {name:name, expression:expression} }

symbol = chars:[A-Za-z]+ { return chars.join("") }

expression = (term _)+

term = terminal / symbol modifier?

terminal = quote chars:chars quote { return chars;}

chars
  = chars:char+ { return chars.join(""); }

char
  = [^"\\\0-\x1F\x7f]

quote
  = "'" / '"'

modifier = op:("+" / "*"/ "?") {return op;}

digits = chars:[0-9]+ { return chars.join("") }

_ "whitespace"
  =  whitespace*

whitespace
  = [ \t]

_r
  = [ \t\r\n]+