;; In Emacs, open this file in -*- Scheme -*- mode.

;; Pascal's triangle

(defrec zip
  (fun (l1 l2)
       (if (list-empty? l1)
           list-empty
           (list-prepend
            (list-prepend (list-head l1) (list-head l2))
            (zip (list-tail l1) (list-tail l2))))))

(defrec %pascal
  (fun (n)
       (if (= n 1)
           (list-make (list-make 1))
           (let* ((p (%pascal (- n 1)))
                  (p1 (zip (list-head p) (list-prepend 0 (list-head p))))
                  (p2 (list-map (fun (pair)
                                     (+ (list-head pair) (list-tail pair)))
                                p1)))
             (list-prepend (list-append p2 (list-make 1)) p)))))

(def pascal (fun (n) (list-reverse (%pascal n))))

(def list-int-print
     (fun (l)
          (char-print '(')
                      (list-for-each (fun (elem)
                                          (int-print elem)
                                          (char-print ' '))
                                     l)
                      (char-print ')')))

(def print-pascal
     (fun (p)
          (list-map
           (fun (l)
                (list-int-print l)
                (newline-print))
           p)))

(defrec tui
  (fun ()
       (string-print "enter size (0 to exit)> ")
       (let ((size (int-read)))
         (if (= size 0)
             0
             (begin
               (print-pascal (pascal size))
               (tui))))))

(tui)