How to replace an item by another in a list in DrScheme when given paramters are two items and a list?

Question

How to replace an item by another in a list in DrScheme when given paramters are two items and a list?

Answer 1

This replaces all the occurrences of fsym in the list lst to the symbol tsym in DrRacket

(define (subst fsym tsym lst)

(cond

[(null? lst) lst]

[eq? (first lst) fsym)(cons tsym (subst fsym tsym (rest lst)))]

[else (cons (first lst)(subst fsym tsym (rest lst)))]))

(subst 'a 'b '(f g a h a))

;the results will be as follows.

'(f g b h b)