List.Chars and String.Chars

Introduction

The List.Chars protocol is used by Kernel.to_charlist to convert a value into a list of characters (think single-quoted string).

The String.Chars protocol is used to convert a value to a string (a binary/double-quoted string). This is the protocol used for string interpolation.

The protocols are implemented identically, except List.Chars requires that we write a to_charlist function, and String.Chars requires we write to_string.

Although we could implement a String.Chars.to_string for our Midi struct, it probably wouldn’t make much sense. What would we interpolate into the string?

Protocols are polymorphism

When we want to write a function that behaves differently depending on the type of its arguments, we’re looking at a polymorphic function.