In Elixir, is there a way to determine if a module exists?

You can use Code.ensure_compiled?/1, but there is a side effect: it will also attempt to load the module if it is not already, which may not be desired (depending on the use-case).

Here is an approach that should work without any side effects:

iex> function_exported?(String, :__info__, 1)
true

iex> function_exported?(NoModule, :__info__, 1)
false

Elixir modules export :__info__/1 so testing for it provides a generic solution.