> id x = x
> id 2
2
> id "Hello!"
"Hello!"

> id = \x -> x
> id 2
2

> fib 0 = 1
> fib 1 = 1
> fib n = fib (n-1) + fib (n-2)

> fib 2
2
> fib 3
3
> fib 4
5