simple_stack.scm

(define (addToStack expr extra_arg)
  (cons expr extra_arg)
)

(define (popStack extra_arg)
  (cond ( (null? (car extra_arg)) '() )
        ( else (cdr extra_arg) )
  )
)

(define (findInStack symbol extra_arg)
  (cond ( (null? extra_arg) '() )
        ( (null? (car extra_arg)) '() )
        ( (equal? symbol (car (car extra_arg))) (cdr (car extra_arg)) )
        ( else (if (null? (cdr extra_arg)) #f
               (findInStack symbol (cdr extra_arg)) )
        )
  )
)

(define (inStack? symbol extra_arg)
  (cond ( (null? extra_arg) #f )
        ( (null? (car extra_arg)) #f )
        ( (equal? symbol (car (car extra_arg))) #t )
        ( else (if (null? (cdr extra_arg)) #f
               (inStack? symbol (cdr extra_arg)) )
        )
  )
)

(addToStack '(myadd 4 5) '())
;(addToStack '(a 10) '())

(inStack? 'l (addToStack '(a 10) '((b 15) (c 20) (z -5) (n 42) (a 20)) )
)

;(popStack (addToStack '(a 10) '((b 15) (c 20) (z -5) (n 42) (a 20)) ) )