Below you’ll find a recursive and an iterative version of the Factorial algorithm in Lisp/Scheme, based on the book Structure and Interpretation of Computer Programs (SICP).

**Recursive**

```
(define (factorial n)
(if (= n 1)
1
(* n (factorial (- n 1) ))
))
(display (factorial 7))
```

**Iterative**

```
(define (factorial n)
(define (iter product counter)
(if (> counter n)
product
(iter (* counter product) (+ counter 1))
))
(iter 1 1))
(display (factorial 7))
```

Notice that in this version the procedure (i.e., the function) is still recursive, as it’s defined in terms of itself. However, since it’s a tail recursion, the Lisp interpreter/compiler will generate an iterative process, where the variables will be kept through out all iterations.

Khushboothis program is given an error

*** – DEFUN: the name of a function must be a symbol, not (FACT N)