49 lines
1.2 KiB
Scheme
49 lines
1.2 KiB
Scheme
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(load "util.scm")
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(load "misc/sicp-regsim.scm")
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(display "\nex-5.20 - box-and-pointer\n")
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(define x (cons 1 2))
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(define y (list x x))
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; | Index | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
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; |-------|---|---|---|---|---|---|---|
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; |the-car| | n1| p1| p1| | | |
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; |the-cdr| | n2| p3| e0| | | |
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(display "[done]\n")
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(display "\nex-5.21 - count-leaves\n")
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(define (count-leaves tree)
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(cond ((null? tree) 0)
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((not (pair? tree)) 1)
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(else (+ (count-leaves (car tree))
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(count-leaves (cdr tree))))))
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(define (not-pair? x) (not (pair? x)))
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(define count-leaves-machine
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(make-machine
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'(tree val continue)
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(list (list 'cons cons) (list 'car car) (list 'cdr cdr)
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(list 'not-pair? not-pair?) (list 'null? null?))
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'(controller
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(assign val (const 0))
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(assign continue (label count-done))
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count-leaves
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(test (op null?) (reg tree))
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(branch (label null-case))
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(test (op not-pair?))
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(branch (label not-pair-case))
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null-case
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not-pair-case
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(goto (reg continue))
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count-done)))
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(set-register-contents! count-leaves-machine 'tree '())
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(start count-leaves-machine)
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(assert (get-register-contents count-leaves-machine 'val) 0)
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(display "\nex-5.22\n")
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