MyVal (version 1)

Documentation on @types, @specs, StreamData, & TypeCheck

Types & Specs:

• https://hexdocs.pm/elixir/typespecs.html
• https://elixir-lang.org/getting-started/typespecs-and-behaviours.html
• https://hexdocs.pm/elixir/1.13.2/typespecs.html

StreamData:

• https://hexdocs.pm/stream_data/StreamData.html
• https://elixirschool.com/en/lessons/libraries/stream-data/
• https://github.com/whatyouhide/stream_data

TypeCheck:

• https://github.com/Qqwy/elixir-type_check
• https://hexdocs.pm/type_check/readme.html
• https://hexdocs.pm/type_check/type-checking-and-spec-testing-with-typecheck.html

Mix.install([
  {:type_check, "~> 0.10.0"},
  {:stream_data, "~> 0.5.0"}
])

Create the MyVal module

defmodule MyVal do
  use TypeCheck
  defstruct [:history]

  @type! t :: %MyVal{history: list(number())}

  def val(%MyVal{history: []}), do: nil

  def val(%MyVal{history: [hd | _tl]}), do: hd

  def add(%MyVal{history: hist} = my_val, new_val) when is_list(hist) do
    val = my_val |> val()
    %{my_val | history: [val + new_val | hist]}
  end

  def subtract(%MyVal{history: hist} = my_val, new_val) when is_list(hist) do
    val = my_val |> val()
    %{my_val | history: [val - new_val | hist]}
  end

  def multiply(%MyVal{history: hist} = my_val, new_val) when is_list(hist) do
    val = my_val |> val()
    %{my_val | history: [val * new_val | hist]}
  end

  def divide(%MyVal{history: hist} = my_val, new_val) when is_list(hist) do
    val = my_val |> val()
    %{my_val | history: [val / new_val | hist]}
  end

  def view(%MyVal{history: _hist} = my_val) do
    %{val: val(my_val), my_val: my_val}
  end
end

(Failed) attempt to override how Elixir displays MyVal instances

defimpl Inspect, for: MyVal do
  def inspect(my_val, _opts) do
    # %MyVal{my_value: #{my_val.value}, history: #{my_val.history}}
    """
    #{my_val |> MyVal.val()}
    """
  end
end

defimpl String.Chars, for: MyVal do
  def to_string(my_val) do
    # %MyVal{my_value: #{my_val.value}, history: #{my_val.history}}
    """
    #{my_val |> MyVal.val()}
    """
  end
end

String.Chars.impl_for([])

Use the MyVal module

%MyVal{history: [7, 3, -8]}
|> MyVal.add(8)
|> MyVal.view()

# |> (fn my_val -> %{val: MyVal.val(my_val), my_val: my_val} end).()
# |> inspect()

%MyVal{history: [7, 3, -8]}
|> MyVal.subtract(8)
|> MyVal.add(11)
|> MyVal.multiply(10)
|> MyVal.subtract(10)
# |> MyVal.divide(10)
|> MyVal.view()