# File lib/sass/script/tree/map_literal.rb, line 50
    def _perform(environment)
      keys = Set.new
      map = Sass::Script::Value::Map.new(Sass::Util.to_hash(pairs.map do |(k, v)|
        k, v = k.perform(environment), v.perform(environment)
        if keys.include?(k)
          raise Sass::SyntaxError.new("Duplicate key #{k.inspect} in map #{to_sass}.")
        end
        keys << k
        [k, v]
      end))
      map.options = options
      map
    end