99 LISP problems: Problem #21 Jun 22nd, 2014 12:47 pm Solution to the 99 LISP Problems #21 1 2 3 4 5 6 7 8 (defun insert-at (new-elem alist n) (let ((i 1)) (mapcan (lambda (x) (let ((j i)) (setf i (1+ i)) (if (= j n) (list new-elem x) (list x)))) alist))) Lisp dialect: Steel Bank Common Lisp