[plt-scheme] Dr.Scheme freezes on (fib 100) recursion

On Jan 7, 2009, at 11:00 PM, Richard Cleis wrote:

> (fib 100) is a big number for that function; it'll take awhile to  
> compute.  Are you sure it is freezing? When you click the stop sign,  
> does the program stop?

Actually, the problem is that you turned a linear computation into an  
exponential one.  Here's one way to solve it:

(require (planet dherman/memoize))

(define/memo (fib n)
  (if (< n 3)
      1
  (+ (fib (- n 1)) (fib (- n 2)))))

(fib 100)

=>

354224848179261915075

John Clements

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