Ch6, Ex12

declare
fun {NewExtensibleArray L H Init}
   A={NewCell {NewArray L H Init}}#Init
   proc {CheckOverOrUnderflow I}
      Arr=@(A.1)
      Low={Array.low Arr}
      High={Array.high Arr}
   in
      if I>High then
         High2=Low+{Max I 2*(High-Low)}
         Arr2={NewArray Low High2 A.2}
      in
         for K in Low..High do Arr2.K:=Arr.K end
         (A.1):=Arr2
      elseif I<Low then
         Low2 = Low - {Max (High-Low) (Low-I)}
         Arr2={NewArray Low2 High A.2}
      in
         for K in Low..High do Arr2.K:=Arr.K end
         (A.1):=Arr2
      end
   end
   proc {Put I X}
      {CheckOverOrUnderflow I}
      @(A.1).I:=X
   end
   fun {Get I}
      {CheckOverOrUnderflow I}
      @(A.1).I
   end
in extArray(get:Get put:Put)
end