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29 lines
655 B
29 lines
655 B
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(in-package :cl-rng)
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(defparameter *default-randomness-provider* #'urandom)
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(defun chance (fraction &key (provider *default-randomness-provider*))
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(< (funcall provider) fraction))
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(export '*default-randomness-provider*)
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(export 'chance)
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(defun weighted (weights &key (default nil) (provider *default-randomness-provider*))
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(let ((previous 0)
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(result (funcall provider))
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(rval default))
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(mapc (lambda (x)
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(let ((value (car x))
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(weight (cdr x)))
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(and (>= result previous)
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(<= result (+ previous weight))
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(setf rval value))
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(incf previous weight)))
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weights)
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(values rval result)))
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(export 'weighted)
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