Check if a flat array is comprised wholly of true or wholly of false values

How can I check if all elements in an array are true, or if all elements are false?

Ideally, I am trying to avoid a really long if expression.

array('a'=> true, 'b'=> true, ...)

To clarify the expected result:

• If the array has both true and false values return nothing.
• If the array has only true values return true.
• If the array has only false values return false.

if(count(array_unique($your_array)) === 1)  
  return current($your_array);

else return;