Simplified isBlank in Clojure
Polymorphic dispatch keyed on the type

Interfaces, in groovy.  You don't get polymorphism in Java without it
being tied to the type.

Does not compile.
A la carte dispatch in clojure

defmulti <name of method> <criterion>
"Configurable" polymorphic dispatch in clojure

Can be triggered off any criteria we want.