picrin/contrib/10.partcont/piclib/partcont.scm

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(define-library (picrin control)
(import (scheme base))
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; based on paper "Representing Monads" (Filinski 1994)
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(define m #f)
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(define (abort t)
(let ((v (t))) ; (t) may update m. do not place me like (m (t))
(m v)))
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(define (reset t)
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(let ((n m))
(call/cc
(lambda (k)
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(set! m (lambda (r)
(set! m n)
(k r)))
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(abort t)))))
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(define (shift h)
(call/cc
(lambda (k)
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(abort
(lambda ()
(h (lambda (v)
(reset (lambda ()
(k v))))))))))
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(export shift
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reset))