Basic operators

In the previous chapter, we saw Elixir provides +, -, *, / as arithmetic operators, plus the functions div/2 and rem/2 for integer division and remainder.

Elixir also provides ++ and -- to manipulate lists:

iex> [1, 2, 3] ++ [4, 5, 6]
[1, 2, 3, 4, 5, 6]
iex> [1, 2, 3] -- [2]
[1, 3]

String concatenation is done with <>:

iex> "foo" <> "bar"
"foobar"

Elixir also provides three boolean operators: or, and and not. These operators are strict in the sense that they expect something that evaluates to a boolean (true or false) as their first argument:

iex> true and true
true
iex> false or is_atom(:example)
true

Providing a non-boolean will raise an exception:

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

or and and are short-circuit operators. They only execute the right side if the left side is not enough to determine the result:

iex> false and raise("This error will never be raised")
false
iex> true or raise("This error will never be raised")
true

Note: If you are an Erlang developer, and and or in Elixir actually map to the andalso and orelse operators in Erlang.

Besides these boolean operators, Elixir also provides ||, && and ! which accept arguments of any type. For these operators, all values except false and nil will evaluate to true:

# or
iex> 1 || true
1
iex> false || 11
11

# and
iex> nil && 13
nil
iex> true && 17
17

# !
iex> !true
false
iex> !1
false
iex> !nil
true

As a rule of thumb, use and, or and not when you are expecting booleans. If any of the arguments are non-boolean, use &&, || and !.

Elixir also provides ==, !=, ===, !==, <=, >=, < and > as comparison operators:

iex> 1 == 1
true
iex> 1 != 2
true
iex> 1 < 2
true

The difference between == and === is that the latter is more strict when comparing integers and floats:

iex> 1 == 1.0
true
iex> 1 === 1.0
false

In Elixir, we can compare two different data types:

iex> 1 < :atom
true

The reason we can compare different data types is pragmatism. Sorting algorithms don’t need to worry about different data types in order to sort. The overall sorting order is defined below:

number < atom < reference < function < port < pid < tuple < map < list < bitstring

You don’t actually need to memorize this ordering; it’s enough to know that this ordering exists.

For reference information about operators (and ordering), check the reference page on operators.

In the next chapter, we are going to discuss pattern matching through the use of =, the match operator.