a simple problem

problem

• write a procedure exp such that (exp x k) evaluates to x to the power k
• exp should be tail-recursive

solution

• code
  (define (exp x k)
  
  (define (helper x k s)(if (= k 0) s
  (helper x (- k 1) (* x s))))
  (helper x k 1))
• note
  helper is defined locally within exp
  
  helper is unbound at the top level

question

• what does (helper x k s) compute? s.xk
• can argue inductively that helper works, then use this result to argue that exp works

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