continuation.scm

;;;; continuation.scm - A better API for continuations
;
; Copyright (c) 2008-2022, The CHICKEN Team
; Copyright (c) 2007, Felix L. Winkelmann
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;
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(declare
  (unit continuation)
  (disable-interrupts))

(foreign-declare "#define C_direct_continuation(dummy) t1")

(module chicken.continuation
  (continuation?
   continuation-capture
   continuation-graft
   continuation-return)

(import scheme chicken.base chicken.fixnum)

(include "common-declarations.scm")

(define (continuation-capture proc)
  (let ((winds ##sys#dynamic-winds)
	(k (##core#inline "C_direct_continuation" #f)))
    (proc (##sys#make-structure 'continuation k winds))))

(define (continuation? x)
  (##sys#structure? x 'continuation))

(define (continuation-graft k thunk)
  (##sys#check-structure k 'continuation 'continuation-graft)
  (let ([winds (##sys#slot k 2)])
    (unless (eq? ##sys#dynamic-winds winds)
      (##sys#dynamic-unwind winds (fx- (length ##sys#dynamic-winds) (length winds))))
    ((##core#primitive "C_continuation_graft") k thunk)))

(define continuation-return
  (lambda (k . vals)
    (##sys#check-structure k 'continuation 'continuation-return)
    ((##core#primitive "C_continuation_graft") k (lambda () (apply values vals))))))