I had a problem where I needed to make sure a string was returned from a function that was part of a with clause. I thought, “You can’t pattern match here, right? That would just be too convenient.”

Turns out you totally can. Here’s an example from the docs.

users = %{"melany" => "guest", "bob" => :admin}

with {:ok, role} when not is_binary(role) <- Map.fetch(users, "bob") do
  {:ok, to_string(role)}
end