pattern.treetop

grammar Pattern
  rule choose
    first:concatenate_or_empty '|' rest:choose {
      def to_ast
        Choose.new(first.to_ast, rest.to_ast)
      end
    }
    /
    concatenate_or_empty
  end

  rule concatenate_or_empty
    concatenate / empty
  end

  rule concatenate
    first:repeat rest:concatenate {
      def to_ast
        Concatenate.new(first.to_ast, rest.to_ast)
      end
    }
    /
    repeat
  end

  rule empty
    '' {
      def to_ast
        Empty.new
      end
    }
  end

  rule repeat
    brackets '*' {
      def to_ast
        Repeat.new(brackets.to_ast)
      end
    }
    /
    brackets
  end

  rule brackets
    '(' choose ')' {
      def to_ast
        choose.to_ast
      end
    }
    /
    literal
  end

  rule literal
    [a-z] {
      def to_ast
        Literal.new(text_value)
      end
    }
  end
end