;; An entry holds a key/value pair
;; for use in Dictionaries.
;;
(define-struct entry (key value))

;; A Dictionary is a structure with two "methods" (fields which are functions):
;; add-fn! and lookup-fn are functions which signatures below.
;;
(define-struct dict (add-fn! lookup-fn))

;; add-fn!: ANY ANY --> ??
;; SIDE-EFFECT: change the contents.
;; We return (the updated) contents, primarily for debugging purposes.

;; lookup: key --> entry or false
;; Does the key occur inside "contents"?
;; If so, return that entry, else return the sentinel false.



;;;;;;;;;;;;;;;;;;

(define new-dict/list
  (local {(define dict-count 0)}
    (lambda ()
      (local {;; a local list-of-entries,
              ;; used only by the dictionary we're creating now:
              ;;
              (define contents empty)
              
              ;; All contracts as per Dictionary above.
              
              (define (add! k val)
                (begin (set! contents (cons (make-entry k val) contents))
                       contents))
              
              (define (lookup key) (lookup-helper key contents))
              
              ;; lookup-helper: key, list-of-entries --> entry or false
              ;; Does the key occur inside "entries"?
              ;; If so, return that entry, else return the sentinel false.
              ;;
              (define (lookup-helper key entries)
                (cond [(empty? entries) false]
                      [(cons?  entries)
                       (cond [(equal? key (entry-key (first entries)))
                              (first entries)]
                             [else (lookup-helper key (rest entries))])]))
              ;
              ; NB this function can be of course easily re-written as a list visitor.
              }
        (begin
          (set! dict-count (add1 dict-count))
          (make-dict add! lookup))))))



(define (new-dict/vec max-key)
  (local {; Our local datastore, for numeric keys: a vector.
          (define data-smallnums (make-vector max-key false))
          
          ; Our local datastore, for 
          (define data-other (new-dict/list))
          
          ;; small-num?: key --> boolean
          ;; Is k a valid key for the vector?
          ;;
          (define (small-num? k) (and (number? k) (<= 0 k) (< k max-key)))
          
          ;; All contracts as per Dictionary above.
          ;; We proceed by using the vector if possible,
          ;; else just forward the call to our other robust dict implementation.

          ;; add!: ANY, ANY --> vector-of-entry or list-of-entry
          ;; Again, the return value is for debugging mroe than anything.
          ;;
          (define (add! k v) 
            (cond [(small-num? k) 
                   (begin (vector-set! data-smallnums k v)
                          data-smallnums)]
                  [else ((dict-add-fn! data-other) k v)]))

          (define (lookup k)
            (cond [(small-num? k) (vector-ref  data-smallnums k)]
                  ; Note how we initialized the vector to contain false -- our sentinel.
                  [else ((dict-lookup-fn data-other) k)]))
          }
    (make-dict add! lookup)))




;;;;;; Tests

; Okay, actually both german and french nouns
; *should* be represented by a structure which includes a gender field.

(define english->german (new-dict/vec 10))

(boolean=? false ((dict-lookup-fn english->german) 'health))
(boolean=? false ((dict-lookup-fn english->german) 1))
(boolean=? false ((dict-lookup-fn english->german) 11))
((dict-add-fn!   english->german) 'health 'gesundheit)
((dict-add-fn!   english->german)  1      'eins)
((dict-add-fn!   english->german) 11      'elf)
((dict-lookup-fn english->german) 'health)
((dict-lookup-fn english->german)  1)
((dict-lookup-fn english->german) 11)



((dict-add-fn!   english->german) 'science 'wissenschaft)
((dict-lookup-fn english->german) 'health)

(define english->french (new-dict/vec 10000))
(boolean=? false
           ((dict-lookup-fn english->french) 'health))
((dict-add-fn!   english->french) 'health 'sante)
((dict-add-fn!   english->french) 'computer 'ordinateur)
((dict-add-fn!   english->french) 'weekend  'weekend)
((dict-lookup-fn english->french) 'health)


((dict-add-fn!   english->german) 'computer-science 'informatik)
((dict-lookup-fn english->german) 'science)
((dict-lookup-fn english->german) 'health)
(boolean=? false
           ((dict-lookup-fn english->german) 'gymnasium))