I am trying to do exercise 2.78 in SICP, but the functions put and get are unknown. I have tried multiple languages, like pretty big, racket, r5rs, mit-scheme, mzscheme, etc. I even downloaded the SICP support (http://www.neilvandyke.org/sicp-plt/), to no avail. How can I get these functions to work?
Yes, I found SICP a little annoying sometimes because of stuff like this. Functions that are assumed to exist but don't actually exist make it harder to try to the examples. I wrote my own (get) and (put) like so (this was in GNU guile):
(define global-array '())
(define (make-entry k v) (list k v))
(define (key entry) (car entry))
(define (value entry) (cadr entry))
(define (put op type item)
(define (put-helper k array)
(cond ((null? array) (list(make-entry k item)))
((equal? (key (car array)) k) array)
(else (cons (car array) (put-helper k (cdr array))))))
(set! global-array (put-helper (list op type) global-array)))
(define (get op type)
(define (get-helper k array)
(cond ((null? array) #f)
((equal? (key (car array)) k) (value (car array)))
(else (get-helper k (cdr array)))))
(get-helper (list op type) global-array))
Probably a naive implementation from the perspective of later in the book, but fairly simple and worked fine.