I recently found out about the match?/2 function in Elixir through the #elixir-lang IRC channel on Freenode.
What this function allows you to do is to determine if a given pattern matches a given expression. For instance, if you wanted to know if a list of maps contained a particular key + value combination, you could do this:
people = [%{name: "John"}, %{name: "Jane"}]
Enum.any?(people, fn (person) -> match?(%{name: "John"}, person) end)
This code will get Elixir to tell you if any of the people have the name “John”. In this case, the result would be true. You could even get fancy and use a shorter function:
Enum.any?(people, &(match?(%{name: "John"}, &1)))
This shorter function defines the same function in the first example, but instead of having a named argument to the function, &1 is used instead.