> Where do I put memo-proc? In the "interpreted space" or "interpreter
> space"? Both choices seem confusing to me.
> If the interpreter was already applicative, how can the same
> expression gets applied more than once?

> (define (memo-proc proc)
>   (let ((already-run? false) (result false))
>     (lambda ()
>       (if (not already-run?)
>           (begin (set! result (proc))
>                  (set! already-run? true)
>                  result)
>           result))))