Type Playground

type_playground.ex

defmodule TypePlayground do
  defmodule Maybe do
    @type t(term) :: {:just, term} | :nothing
  end

  defmodule Result do
    @type t(term) :: {:ok, term} | {:error, atom}
  end

  defmodule ApiAction do
    defstruct func: nil

    @type func :: (String.t() -> String.t())
    @type t :: %__MODULE__{func: func}

    @spec run(t, String.t()) :: String.t()
    def run(action, string) do
      IO.puts("Before: #{string}")
      result = action.func.(string)
      IO.puts("After: #{result}")
      result
    end
  end

  @spec greeting(Maybe.t(String.t())) :: Maybe.t(String.t())
  def greeting(term) do
    term
  end

  def foo do
    greeting({:just, "hello"})
  end

  @spec bar(Result.t(String.t())) :: Result.t(String.t())
  def bar(term) do
    term
  end
end