;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-advanced-reader.ss" "lang")((modname lect12-scheme-versions-of-prolog) (read-case-sensitive #t) (teachpacks ((lib "universe.ss" "teachpack" "2htdp"))) (htdp-settings #(#t constructor repeating-decimal #t #t none #f ((lib "universe.ss" "teachpack" "2htdp")))))
;;;;; some scope examples:
(define (make-adder n)
  (lambda (m) (+ n m)))

; Two examples of applying this function:
;
(make-adder 4)     ; evals to (lambda (m) (+ m 4))
((make-adder 3) 4) ; evals to 7



(let {[x 5]} (+ x (let {[x 3]} x)))
(let {[x 5]} (let {[x (+ x 1)]} x))
(let {[y 5]}
  (let {[x (+ y 1)]}
    (* y x)))




;;;;; Some functions to also implement in prolog:
(define (my-length data)
  (cond [(empty? data) 0]
        [(cons? data) (+  (my-length (rest data)) 1)]))




(define (length2 data)
  (length2-help 0 data))

; Return the #items in data + len-so-far.
;
(define (length2-help len-so-far data)
  (cond [(empty? data) len-so-far]
        [(cons? data) (length2-help (+ 1 len-so-far) (rest data))]))
  

(check-expect (length2 empty) 0)
(check-expect (length2 (list 'a)) 1)
(check-expect (length2 (list 'a 'b)) 2)
(check-expect (length2 (list 'a 'b 'c 'd 'e)) 5)



(define (my-list-ref idx data)
  (cond [(empty? data) ...]
        [(cons? data) ...idx...(my-list-ref ___ (rest data))]))

(check-expect (my-list-ref 0 (list 'hi)) 'hi)
(check-expect (my-list-ref 0 (list 'hi 'bye 'aloha 'ciao)) 'hi)
(check-expect (my-list-ref 1 (list 'hi 'bye 'aloha 'ciao)) 'bye)
(check-expect (my-list-ref 3 (list 'hi 'bye 'aloha 'ciao)) 'ciao)

(check-error (my-list-ref 0 empty) "idx too big")
(check-error (my-list-ref 1 empty) "idx too big")
(check-expect (my-list-ref 1 (list 'hi)) "idx too big")
(check-expect (my-list-ref 4 (list 'hi 'bye 'aloha 'ciao)) "idx too big")