[Fixnum]

Be careful -- this doesn't fully memoize recursive functions unless you force the computation of intermediate results, since the recursive calls don't use memoization:

(define memo-fib (memoize fib)) ;; example from SICP (memo-fib 40) ;; long wait

I would love to see a good general-purpose 'memoize but rather doubt it's possible, though I think I remember seeing one in Common Lisp in "Paradigms of Artificial Intelligence Programming" that exploited CL's weird namespacing rules for functions to make recursive functions like 'fib run fast.

[kenko]

You can solve the problem with the parent's memoization by writing the original fib using open recursion and closing it with a fixed-point operator. Doesn't help for library functions or things like that, though.

[soegaard]

http://planet.racket-lang.org/package-source/dherman/memoize...