zestime

(list 'a 'b 'c) ; '(a b c)
(list (list 'george)) ; '((george))
(cdr '((x1 x2) (y1 y2)))  ; '((y1 y2))
(cadr '((x1 x2) (y1 y2))) ; '(y1 y2)
(pair? (car '(a short list))) ; #f
(memq 'red '((red shoes) (blue socks))) ; #f
(memq 'red '(red shoes blue socks)) ; '(red shoes blue socks)

zestime

(define (myequal? col1 col2)
  (if (and (pair? col1) (pair? col2))
      (and (eq? (car col1) (car col2)) (myequal? (cdr col1) (cdr col2)))
      (eq? col1 col2)))
 
(myequal? '(this is a list) '(this is a list))  ; #t
(myequal? '(this is a list) '(this (is a) list))  ; #f

zestime

(define (element-of-set? x set)
  (cond ((null? set) false)
        ((equal? x (car set)) true)
        (else (element-of-set? x (cdr set)))))


(define (adjoin-set x set)
  (if (element-of-set? x set)
      set
      (cons x set)))

zestime

; No change, as same as before
(define (element-of-set? x set)
  (cond ((null? set) false)
        ((equal? x (car set)) true)
        (else (element-of-set? x (cdr set)))))

; Just use cons, don't need to use element-of-set anymore
(define (adjoin-set x set)
  (cons x set))

zestime

(define (make-accumulator init)
  (lambda (value)
    (begin (set! init (+ init value))
           init)))

zestime

(define (make-account balance key)
  (define (withdraw amount)
    (if (>= balance amount)
        (begin (set! balance (- balance amount))
               balance)
        "Insufficient funds"))
  (define (deposit amount)
    (set! balance (+ balance amount))
    balance)
  (define (dispatch k m)

zestime

(define (make-account balance key)
  (let ((try 0))
    (define (withdraw amount)
      (if (>= balance amount)
          (begin (set! balance (- balance amount))
                 balance)
          "Insufficient funds"))
    (define (deposit amount)
      (set! balance (+ balance amount))
      balance)

zestime

>>> import re
>>> msg1 = "aaabbbccc"
>>> msg2 = "dddbbbeee"
>>> re.findall("bbb(?=ccc)", msg1) # lookahead
['bbb']
>>> re.findall("bbb(?=ccc)", msg2)
[]
>>> re.findall("bbb(?!ccc)", msg1) # negative lookahead
[]
>>> re.findall("bbb(?!ccc)", msg2)

zestime

> /bbb(?=ccc)/.exec("aaabbbccc") // lookahead
["bbb"]
> /bbb(?=ccc)/.exec("dddbbbeee")
null
> /bbb(?!ccc)/.exec("aaabbbccc") // negative lookahead
null
> /bbb(?!ccc)/.exec("dddbbbeee")
["bbb"]
> /(?<=aaa)bbb/.exec("aaabbbccc") // lookbehind?
 Uncaught SyntaxError: Invalid regular expression: /(?<=aaa)bbb/: Invalid group

zestime

> /(aaa)bbb/.exec("aaabbbccc") // lookbehind?
["aaabbb", "aaa"]
> /([^a]{3})bbb/.exec("dddbbbeee") // negative lookbehind?
["dddbbb", "ddd"]