Correct, `use` is a part of Elixir. When you `use` a module like `use FooModule`, it runs the `__using__` macro defined in `FooModule`. Because `__using__` is a macro, it serves as an extension point that allows modules that define it to "inject" code into the modules that `use` it. This injected code could be anything: function definitions, constants, module definitions, etc.

For example:

  defmodule A do
    defmacro __using__(_env) do
      quote do
        defmodule Math do
          def plus_itself(y) do
            y + y
          end
        end
      end
    end
  end

  defmodule B do
    use A
  end

  B.Math.plus_itself(10) |> IO.inspect() #=> 20

More info: https://hexdocs.pm/elixir/alias-require-and-import.html#use

Two quite different things!

Elixir’s use: https://hexdocs.pm/elixir/main/alias-require-and-import.html...

Gleam’s use: https://tour.gleam.run/advanced-features/use/

I don't know how use works in gleam but, at first brush they seem very different. Use in elixir basically allows you to execute a macro callback in the module `use`ing the other module. In gleam it seems to be a tool for chaining function calls (maybe closer to `with` in elixir?).