abstract class Parser[I, T] {+
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  def parse(ts: I): Set[(T, I)]+
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+
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  def parse_all(ts: I) : Set[T] =+
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    for ((head, tail) <- parse(ts); if (tail.isEmpty)) +
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      yield head+
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+
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  def || (right : => Parser[I, T]) : Parser[I, T] = +
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      new AltParser(this, right)+
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  def ==>[S] (f: => T => S) : Parser [I, S] = +
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      new FunParser(this, f)+
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}+
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+
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+
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