[cess11]

Elixir won't allow you to do that:

   iex(2)> "/home/cess11" * 9
   ** (ArithmeticError) bad argument in arithmetic expression: "/home/cess11" * 9
       :erlang.*("/home/cess11", 9)
       iex:2: (file)

Documentation is full of type information:

https://hexdocs.pm/elixir/Enum.html#types

[self]

I think their point is that Elixir lets you write

    defmodule Multiply do
      def m9(m1), do: m1 * 9
    end

    # elsewhere...
    defmodule Caller do
      def doit() do
        Multiply.m9(2)
        Multiply.m9("hi")
      end
    end

It won't raise an exception or give you a warning while compiling it (tested with 1.18.4). Even adding

    @spec m9(integer()) :: integer()

above its definition doesn't do anything.