(define-module (nql)
  #:use-module (srfi srfi-13)
  #:export (nql
	    paren->number))


(define (nql str count-all?)
  "GIven string of parens STR,
calculates '(' - ')' when
COUNT-ALL is #t..

If COUNT-ALL? is #f, returns the
index of the first time a negative
number is reached."
  (let loop ((floor 0) (iteration 0) (lst (map paren->number
					       (string->list str))))
    (cond
     ((and (not count-all?)
	   (> 0 floor)) iteration)
     ((null? lst) (and count-all? floor))
     (#t (loop (+ (car lst) floor)
	       (1+ iteration)
	       (cdr lst))))))

(define (paren->number char)
  "Given a character representing a
parenthesis, returns 1 for '(' and
-1 for ')'.
Returns zero for all other characters."
  (cond
   ((char=? char #\() 1)
   ((char=? char #\)) -1)
   (#t 0)))