📝Ad hoc hierarchy system
Clojure has an ad hoc hierarchy system. You can define a relationship between any two objects using derive function:
(derive ::rect ::shape)
(derive ::square ::rect)
(derive java.util.Map ::collection)
parents, ancestors, descendants, isa? and § Multiple dispatch in Clojure work with this hierarchy.
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This might be the simplest form of nominal subtyping.