A Procedure that Makes Closures

> (define (make-toggle on-value off-value)

(let ((bit 0))

(lambda ()

(set! bit (- 1 bit))

(if (= bit 1) on-value off-value)

) ) )

> (define traffic-light

(make-toggle 'green 'red) )

> (traffic-light)

red

> (traffic-light)

green

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