Recursing in a lambda function

Question

I have the following 2 functions that I wish to combine into one:

(defun fib (n)
  (if (= n 0) 0 (fib-r n 0 1)))

(defun fib-r (n a b)
  (if (= n 1) b (fib-r (-          


        

Answer 1

LET conceptually binds the variables at the same time, using the same enclosing environment to evaluate the expressions. Use LABELS instead, that also binds the symbols f0 and f1 in the function namespace:

(defun fib (n)
  (labels ((f0 (n) (if (= n 0) 0 (f1 n 0 1)))
           (f1 (a b n) (if (= n 1) b (f1 (- n 1) b (+ a b)))))
    (f0 n)))