Explicit State

declare Counter =

local C = {NewCell 0}

in

fun {$}

OldValue={Access C}

NewValue=OldValue + 1

in

{Assign C OldValue}

NewValue

end

end

{Show {Counter}} % 1

{Show {Counter}} % 2

Oz

(define counter

(let ((c 0))

(lambda ()

(let ((oldValue c)

(newValue

(+ oldValue 1))

(begin

(set! C newValue)

newValue))))

(counter) ;; 1

(counter) ;; 2

Scheme

Implicit State

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