geometry.ex

defmodule Geometry do
    @moduledoc "geometric formulae"
    import IO

    defmodule Quad do
        @moduledoc "Quadilateral formulae"

        defmodule Rect do
            # can't import Geometry
            # since inner modules are loaded before outer ones

            @doc "area of rect"
            @spec area(number, number) :: number
            def area(a, b) do
                Geometry.area(a, b)
            end
        end

        defmodule Square do
            import Rect
            # since Square imports Rect,
            # it can only be defined after Rect

            @doc "area of square"
            @spec area(number) :: number
            def area(a) do
                puts "delegating to rectangle" # inner modules inherit imports
                area(a, a)
            end
        end

    end

    defmodule Circle do
        @pi 3.14

        @doc "area of circle"
        @spec area(number) :: number
        def area(r) do
            Geometry.area(@pi, r*r)
        end
    end

    @doc "area of geometric shape"
    @spec area(number, number) :: number
    def area(a, b) do
        prod(a, b)
    end

    @spec prod(number, number) :: number
    defp prod(a, b\\0) do
        a*b
    end

end