;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-intermediate-lambda-reader.ss" "lang")((modname dictionary-examples) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))

"using association lists (or 'a-lists'):"
(define alist1 '(("three" 3)
                 ("four" 4)
                 ("five" 5)))

; retrieve from an a-list:
(assoc "four" alist1)  ;->  (list "four" 4)    (which is also writable as '("four" 4))
(assoc "seven" alist1) ;->  #false

; Add to an a-list
(define alist2 (cons (list "four" 44) alist1)) ; just cons a new entry on the front
(second (assoc "four" alist2))  ;->  44



""
"using hash tables (immutable):"
; From the student-languages, import the hash-table functions with:
(require "student-extras.rkt")

(define hash-table1 #hash(("three" . 3) ("four" . 4) ("five" . 5)))

; retrieve from a hash:
(hash-ref hash-table1 "four")                  ;-> 4
;(hash-ref hash-table1 "seven")                ;-> ERROR, no such key
(hash-has-key? hash-table1 "seven")            ;-> #false
(hash-ref hash-table1 "seven" 'my-own-default) ;-> 'my-own-default

; Add to a hash-table:
(define hash-table2 (hash-set hash-table1 "four" 44))
(hash-ref hash-table2 "four")  ;-> 44





#| @license: CC0
   @author: ibarland@radford.edu
   @version: 2020-apr-27
|#