Hi Linas, I tried to refactor the function to make it tail recursive but I am repeatedly getting error. The following is the change i made

```
(define* (random-string str-length #:optional (str "")) 
	(define alphanumeric "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")
	(if (> str-length 0)
		((set! str (string-append str (string (string-ref alphanumeric (random (string-length alphanumeric))))))
		(random-string (- str-length 1) str))
		str
	)
)
```
and the error i am getting is.

<unnamed port>:47:0: In procedure random-string:
<unnamed port>:47:0: Wrong type to apply: #<unspecified>