Naive fibonacci is a much more interesting example for memoize than factorial:
fib = +lambda {|n| return 1 if n <= 1; fib[n-2] + fib[n-1]} fib = +lambda {|n| return 1 if n <= 1; fib[n-2] + fib[n-1]} fib = +lambda {|n| return n if n <= 1; fib[n-1] + fib[n-1] }