Rotate list

Write a function with type:

rotate : int -> 'a list -> 'a list

such that rotate n l rotates the list l by n positions to the left. For instance, rotating the list [1;2;3] by 1 position yields [2;3;1].

Other examples are shown by the following asserts:

assert(rotate 0 [5;6;7;8] = [5;6;7;8]);;  
assert(rotate 1 [5;6;7;8] = [6;7;8;5]);;  
assert(rotate 2 [5;6;7;8] = [7;8;5;6]);;  
assert(rotate 3 [5;6;7;8] = [8;5;6;7]);;  
assert(rotate 4 [5;6;7;8] = [5;6;7;8]);;