Write a recursive function that takes an array of words and returns an array that contains all the words capitalized.

If this is the input array:

$[\text{'}$foo$\text{'},$ 'bar', 'world', 'hello'$]$

The output array should be:

$[\text{'}$FOO$\text{'},$ 'BAR', 'WORLD', 'HeLlo'$]$

Here is a hint: Run the following snippet of code. $[0]$ is first position as we've done before. The $[1$:$]$ returns the rest of the list. Now what

happens if you use that as a recursive argument passed back into a function? 'red', 'blue', 'green', 'black'. What is now $[0]?$ etc etc.

arr$[0].$upper$()$ is ok to use in this case.