Programming Erlang, 2nd Edition

Booleans

There is no distinct boolean type in Erlang; instead, the atoms true and false are given a special interpretation and are used to represent boolean literals.

Sometimes we write functions that return one of two possible atomic values. When this happens, it’s good practice to make sure they return a boolean. It’s also a good idea to name your functions to make it clear that they return a boolean.

For example, suppose we write a program that represents the state of some file. We might find ourselves writing a function file_state(File) that returns open or closed. When we write this function, we could think about renaming the function and letting it return a boolean. With a little thought we could rewrite our program to use a function called ...