note 117619 rejected from function.is-array by cmb

Note Submitter: abhardwaj dot aastha at gmail dot com ---- functions like is_array,is_bool etc are generally used in if,elseif statements.Since they return a Boolean value,then why cant we store that Boolean value in a variable or display it?? $a=10; $b=is_array ($a); echo $b; This code is not showing any error but not displaying the Boolean value.What is the reason behind it??