Define some primitives:

(define (square x) (* x x)) (define (compose f g) (lambda (x) (f (g x))))

Define the procedure:

```
(define (repeat f n)
(if (< n 1)
(lambda (x) x)
(compose f (repeat f (- n 1)))))
```

Test with:

```
((repeat square 2) 5)
```

Output:

625

Another solution using the linear iterative way.

```
(define (repeat f n)
(define (iter n result)
(if (< n 1)
result
(iter (- n 1) (compose f result))))
(iter n identity))
```

Note: This is not linearly iterative as described in the book as a chain of *deferred operations* is still being built.

The above answer does not follow the book's instructions. The book instructs "Write a procedure that takes as inputs a procedure that computes f and a positive integer n and returns the procedure that computes the nth repeated application of f." A correct answer is as follows:

```
(define (repeated f n)
(lambda (x) (cond ((= n 0) x)
(else
((compose (repeated f (- n 1)) f) x)))))
```

I think the following solution is more elegant. When we only need to apply the function once, we can just return the function (I'm not doing error-checking here to see of n is smaller than 1).

```
(define (repeated f n)
(if (= n 1)
f
(compose f (repeated f (- n 1)))))
```

<< Previous exercise (1.42) | Next exercise (1.44) >>