Palindrome

Write a function is_palindrome that checks if a list is palindrome. A list is palindrome when it reads the same backwards as forwards.

The function must have the following type:

is_palindrome : 'a list -> bool

Here are some unit tests:

assert(is_palindrome []);;
assert(is_palindrome ['a';'n';'n';'a']);;
assert(is_palindrome ['r';'a';'d';'a';'r']);;
assert(is_palindrome ['a';'n';'n';'e'] = false);;
assert(is_palindrome ['z';'a';'n';'n';'a'] = false);;