By what mechanism is this fibonacci-function memoized?
fib = (map fib' [0..] !!)
where fib' 1 = 1
fib' 2 = 1
fib' n = fib (n-2) + fib (n-1)
And on a related note, why is this version not?
fib n = (map fib' [0..] !! n)
where fib' 1 = 1
fib' 2 = 1
fib' n = fib (n-2) + fib (n-1)