54 lines
1.4 KiB
Scheme
54 lines
1.4 KiB
Scheme
;; In Emacs, open this file in -*- Scheme -*- mode.
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;; Pascal's triangle
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(defrec zip
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(fun (l1 l2)
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(if (list-empty? l1)
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list-empty
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(list-prepend
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(list-prepend (list-head l1) (list-head l2))
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(zip (list-tail l1) (list-tail l2))))))
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(defrec %pascal
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(fun (n)
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(if (= n 1)
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(list-make (list-make 1))
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(let* ((p (%pascal (- n 1)))
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(p1 (zip (list-head p) (list-prepend 0 (list-head p))))
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(p2 (list-map (fun (pair)
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(+ (list-head pair) (list-tail pair)))
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p1)))
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(list-prepend (list-append p2 (list-make 1)) p)))))
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(def pascal (fun (n) (list-reverse (%pascal n))))
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(def list-int-print
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(fun (l)
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(char-print '(')
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(list-for-each (fun (elem)
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(int-print elem)
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(char-print ' '))
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l)
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(char-print ')')))
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(def print-pascal
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(fun (p)
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(list-map
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(fun (l)
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(list-int-print l)
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(newline-print))
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p)))
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(defrec tui
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(fun ()
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(string-print "enter size (0 to exit)> ")
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(let ((size (int-read)))
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(if (= size 0)
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0
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(begin
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(print-pascal (pascal size))
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(tui))))))
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(tui)
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