generator

gen.scm

(define (generator func)
    (define done #f)
    (define res '())
    (define return '())
    (define next (lambda (val)
        (func yield)
    ))
    (define (yield val)
        (if done
            (error "generator already closed")
            (call/cc (lambda (cont)
                (set! next cont)
                (return val)
            ))
        )
    )
    (lambda (val)
        (if done
            res
            (call/cc (lambda (cont)
                (set! return cont)
                (set! res (next val))
                (set! done #t)
                res
            ))
        )
    )
)

(define (gen-func yield)
    (define x (yield 1))
    (yield (* 2 x))
    (yield 3)
    4
)

(define gen (generator gen-func))

(print (gen '())) ; 1
(print (gen 100)) ; 200
(print (gen '())) ; 3
(print (gen '())) ; 4
(print (gen '())) ; 4