Programming Elixir ≥ 1.6

Built-in Protocols

Elixir comes with the following protocols:

• Enumerable and Collectable
• Inspect
• List.Chars
• String.Chars

To play with these, let’s work with MIDI files.

A MIDI file consists of a sequence of variable-length frames. Each frame contains a four-character type, a 32-bit length, and then length bytes of data.^[38]

We’ll define a module that represents the MIDI file content as a struct, because the struct lets us use it with protocols. The file also defines a submodule for the individual frame structure.

protocols/midi.exs

defmodule Midi do

  defstruct(content: <<>>)

  defmodule Frame do
    defstruct(
      type:   "xxxx",
      length: 0,
      data:   <<>>
    )

    def to_binary(%Midi.Frame{type: type, length: length, data: ...