RosettaCodeData/Task/Anonymous-recursion/WDTE/anonymous-recursion.wdte

let str => 'strings';

let fib n => switch n {
  < 0 => str.format 'Bad argument: {q}' n;
  default => n -> (@ memo s n => switch n {
    == 0 => 0; == 1 => 1;
    default => + (s (- n 1)) (s (- n 2));
  });
};