Question

Write a Racket function named listlen that takes a list as a parameter and evaluates to the number of elements in the list. For example (listlen empty) should evaluate to 0 and (listlen '(1 2 3)) should eveluate to 3.

Answer 1

We defined listlen function using define keyword and listpara is the variable decalred for the list parameters and empty? checks if the list is empty and return 0 if not it will return the length of the list and length is a predefined function

Racket code:

#lang racket
(define (listlen listpara)
  (cond
   [(empty? listpara) 0]
   [else (length(listpara))]
)
)

Sample outputs:

> (listlen empty)
0

> (listlen (list 1 2 3 4))
4