Creating an efficent power function- OZ

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Powerbasic

I need to create a power function in oz by by reusing the intermediate results. For example, calculating 2^8 in 3 calculations by saying 2^2 = 2*2, 2^4 = 2^2 * 2^2, 2^8 = 2^4 * 2^4. What I have so far:

declare
proc  {Powerp N M K}
    if M == 0 then K = 1
    elseif M == 1 then K = N
    else
      {Powerp K M-1 K}
      K = N*N
    end
end

It is accepted by emacs but wont display a value in the browser. The input looks something like this:
{Browse {Powerp 2 3}}