;Counts the number of right and left parenthesis in 
;a given list.
;Recurses down each sub-list of the argument list, ls
;returns 2 for each ()
;returns (count-parens (car ls)) + 
;        (count-parens (cdr ls) for each list.
(define count-parens-all
  (lambda (ls)
    ;(display ls) (newline)
    (cond
      ((not (list? ls)) '("Error: argument must be a list"))
      ((null? ls) 2)
      (else
        (cond
          ((atom? (car ls))
            (count-parens-all (cdr ls))
          )
          (else
            (+ (count-parens-all (car ls))
                    (count-parens-all (cdr ls))
            )
          ))))))  
  
;============== Unit Tests ======================
(load "atom.scm")
(load "test.scm")
(load "writeln.scm")
(define msg "count-parens-all")
(test msg (count-parens-all '()) '2) 
(test msg (count-parens-all '((a b) c)) '4)
(test msg (count-parens-all '(((a () b) c) () ((d) e))) '14)
(test msg (count-parens-all '((((a))))) '8)
(test msg (count-parens-all 'a) '("Error: argument must be a list"))