proc
>> multiply = -> x, y { x * y } => #<Proc (lambda)> >> multiply.call(6, 9) => 54 >> multiply.call(2, 3) => 6 >> multiply[3, 4] => 12
>>> sorted([3, -2, -4, 5, 1], key=lambda x: abs(x)) [1, -2, 3, -4, 5]