I believe `one?` would be a useful Enum function. It exists in Ruby's Enumerable module. It invokes a given function for each item in the enumerable and returns true if exactly one invocation returns a truthy value. It returns false otherwise.
This function tests for uniqueness or singularity. Unlike other uniqueness queries, it is concerned with the satisfaction of some criteria (expressed in the function argument) instead of an item's identity.
It is useful in Ruby. Do you think it has a place in Elixir?