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;;;; Under Creative Commons Attribution-ShareAlike 4.0
;;;; International. See
;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
;;; pascal's fucking triangle.
(define-module (one twelve)
#:export (compute-triangle
compute-line
display-line
value-at
print-triangle
print-line))
(define (compute-triangle n)
(cond ((= n 1) (list (compute-line n 1)))
(else (cons (compute-line n 1)
(compute-triangle (- n 1))))))
(define (compute-line n pos)
(cond ((> pos n) '())
(else
(cons (value-at n pos)
(compute-line n (+ pos 1))))))
(define (value-at line pos)
(cond ((= line 1) 1)
((= pos 1) 1)
((= line pos) 1)
(else (+
(value-at (- line 1) (- pos 1))
(value-at (- line 1) pos)))))
;;;; printing
(define (print-triangle tl level)
(cond ((= (length tl) 0) #t)
(else
(print-triangle (cdr tl) (+ 1 level))
(print-line (car tl) level))))
(define (print-line l level)
(let* ((l (map number->string l))
(spaces (string-join (make-list level " ") ""))
(line (string-append spaces (string-join l))))
(format #t "~a\n" line)))
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