class Racc::Grammar::DefinitionEnv

def method_missing(mid, *args, &block)
  unless mid.to_s[-1,1] == '='
    super   # raises NoMethodError
  end
  target = @grammar.intern(mid.to_s.chop.intern)
  unless args.size == 1
    raise ArgumentError, "too many arguments for #{mid} (#{args.size} for 1)"
  end
  _add target, args.first
end