Racket examples - various implementations of list-length

gistfile1.rkt

#lang racket

(require racket/trace)


;; Recursive implementation of list length

(define (list-length l)
  (if (empty? l)
      0
      (+ 1 (list-length (cdr l)))))

(trace list-length)

(display (list-length '(1 2 3 4 5))) ;; should be 5

;; Iterative implementation of list length

(define (list-length-iter l acc)
  (if (null? l)
      acc
      (list-length-iter (cdr l) (+ 1 acc))))
  
(define (list-length-2 l)
  (list-length-iter l 0))

(trace list-length-iter)

(display (list-length-2 '(1 2 3 4 5))) ;; should be 5


;; Recursive implementation of list length using pattern matching

(require racket/match)

(define (list-length-3 l)
  (match l
    ['() 0]
    [(list-rest _ b) (+ 1 (list-length-3 b))]))

(trace list-length-3)

(list-length-3 '(foo bar baz)) ;; should be 3