87 lines
2.0 KiB
Scheme
87 lines
2.0 KiB
Scheme
;;; DDERIV -- Table-driven symbolic derivation.
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;;; Returns the wrong answer for quotients.
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;;; Fortunately these aren't used in the benchmark.
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(define (lookup key table)
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(let loop ((x table))
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(if (null? x)
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#f
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(let ((pair (car x)))
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(if (eq? (car pair) key)
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pair
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(loop (cdr x)))))))
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(define properties '())
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(define (get key1 key2)
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(let ((x (lookup key1 properties)))
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(if x
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(let ((y (lookup key2 (cdr x))))
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(if y
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(cdr y)
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#f))
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#f)))
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(define (put key1 key2 val)
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(let ((x (lookup key1 properties)))
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(if x
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(let ((y (lookup key2 (cdr x))))
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(if y
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(set-cdr! y val)
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(set-cdr! x (cons (cons key2 val) (cdr x)))))
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(set! properties
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(cons (list key1 (cons key2 val)) properties)))))
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(define (my+dderiv a)
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(cons '+
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(map dderiv (cdr a))))
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(define (my-dderiv a)
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(cons '-
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(map dderiv (cdr a))))
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(define (*dderiv a)
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(list '*
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a
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(cons '+
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(map (lambda (a) (list '/ (dderiv a) a)) (cdr a)))))
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(define (/dderiv a)
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(list '-
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(list '/
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(dderiv (cadr a))
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(caddr a))
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(list '/
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(cadr a)
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(list '*
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(caddr a)
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(caddr a)
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(dderiv (caddr a))))))
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(put '+ 'dderiv my+dderiv)
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(put '- 'dderiv my-dderiv)
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(put '* 'dderiv *dderiv)
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(put '/ 'dderiv /dderiv)
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(define (dderiv a)
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(if (not (pair? a))
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(if (eq? a 'x) 1 0)
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(let ((f (get (car a) 'dderiv)))
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(if f
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(f a)
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(fatal-error "No derivation method available")))))
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(define (main . args)
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(run-benchmark
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"dderiv"
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dderiv-iters
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(lambda (result)
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(equal? result
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'(+ (* (* 3 x x) (+ (/ 0 3) (/ 1 x) (/ 1 x)))
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(* (* a x x) (+ (/ 0 a) (/ 1 x) (/ 1 x)))
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(* (* b x) (+ (/ 0 b) (/ 1 x)))
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0)))
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(lambda (a) (lambda () (dderiv a)))
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'(+ (* 3 x x) (* a x x) (* b x) 5)))
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