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cansardhent r-y-lt-ha fnn5i g! ez Il uzIt 2:(30 pr(Qti) Ju howu x'grbdu: ud ghu: b: upg b; h ugogb'(ug, sst!)x' gb bur Vo guogu, whx h oWbws us gb ho'gu ghu bx'dx'gs b; vorxobWus. fbh ugh us xg wbuld bu 'xu gp bu obW gb u?db b?u b; ghusu h ugogxb's, whx: h h uo's wu wb uvd ,uud sbh u woy b; ruh uh burx'g whog ghu pruvxb us voWuu wo i b'Sxdur ghu ;bWbwx'g: b cu (define (set! -start val) (define old 1O) (let ((current val)) (cond ((eq? action value) current (set! old (cons current old)) rent (car new)) current) ((eq? action 'reset) (set! current (car old)) (set! old (cdr old)) else (error "i dont know how to do" action))))) (define (set!-careful var val) (var ]new val)) (define (set! -undo var) (var reset)) Udur ghs )uw s: huh u, o vorxobWu xs o: guoWy o prb: uduru, sb gb gug xgs voWuu, wu jusg uud gb sud (define foo (set!-start 5) (set!-careful foo 10 (set!-careful foo 15) (set!-undo foo)￾         !  : )-  )    ?!!&  B   & ,)) ,% %  ) ) 0%  -0%! %  , 0   0 0     )% %& ,)) % , ,  % ,.  0 ,) ) -% - ,%! % ) , 2 ￾ ￾   ￾  ￾ ￾ ￾￾   ￾ ￾    ￾  ￾￾!     ￾￾!    ￾  ￾    ￾  ￾    ￾￾!    ￾  ￾   ￾  ￾    ￾ ￾ "  #      ￾ ￾    ￾   ￾ ￾   ￾  D )% , %)&  -0 % .  & %   % -& , 1%   %   %%&  <2 ￾  ￾  $ ￾   $ ￾   %& ￾   %& ￾   %$ ￾   %$ ￾   ￾   %&
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