Named Let example from http://docs.racket-lang.org/guide/let.html

Named Let

#lang racket

;; Named let (Section '4.6.4 Named let' of 
;; http://docs.racket-lang.org/guide/let.html)

(define (duplicate-shorthand pos lst)
  (let dup ([i 0]
            [lst lst])
   (cond
    [(= i pos) (cons (car lst) lst)]
    [else (cons (car lst) (dup (+ i 1) (cdr lst)))])))

(duplicate-shorthand 1 (list "apple" "cheese burger!" "banana"))


(define (duplicate-longhand pos lst)
  (letrec ([dup (lambda (i lst)
                (cond
                  [(= i pos) (cons (car lst) lst)]
                  [else (cons (car lst) (dup (+ i 1) (cdr lst)))]))])
    (dup 0 lst)))

(duplicate-longhand 1 (list "apple" "cheese burger!" "banana"))