Programmer Passport: Elixir

Booleans and Truthy Expressions

Elixir has two Boolean values, and you’ve already seen they’re expressed as atoms. Here’s a quick overview of Booleans in Elixir:

• Elixir allows pure Boolean with and, or, and not.
• Elixir allows truthy Boolean operations à la C and Ruby with && and ||.
• Elixir also allows bitwise Boolean operators, but you need a library.
• There’s excellent documentation^[8] for the rest.

This tiny error provides some quick proof of these concepts in IEx:

iex(1)> nil && true
nil
iex(2)> nil and true
** (BadBooleanError) expected a boolean on left-side of "and", got: nil

iex(2)> nil || true
true
iex(3)> !nil
true
iex(4)> not nil
** (ArgumentError) argument error
    :erlang.not(nil)

In Elixir’s truthy expressions, ...