Using racket to return the list of animal's name corresponding to the given animal list

Question

I'm now using racket to build the function that return the list of animal's name corresponding to the given animal list. But there comes a problem.

(define (name-pets l)
    (cond
        [(eq? "dog" first(l)) (append 'happy (name-pets (rest (l))))]
        [(eq? "cat" first(l)) (append 'smart (name-pets (rest (l))))]
        [(eq? "pig" first(l)) (append 'pinky (name-pets (rest (l))))]
        [else (append 'unnamed (name-pets (rest (l))))]))
(name-pets (list "pig" "cat" "dog" "dolphin"))

And when I ran the code,

application: not a procedure; expected a procedure that can be applied to arguments
given: '("pig" "cat" "dog" "dolphin")
arguments...: [none]

What is the problem?

Possible duplicate of My code signals the error "application: not a procedure" or "call to non procedure" — Sylwester

soegaard soegaard · Accepted Answer · 2018-02-28T19:01:13

Change first(l) to (first l) and (rest (l)) to (rest l). Note that you can't insert extra parentheses in Racket. The syntax (l) means call l, but since l is a list and not a function, you run into problems.

Using racket to return the list of animal's name corresponding to the given animal list

1 Answers