Operators reference

Source: Elixir reference, Operators reference.

How operators are parsed, defined and overridden.

General operators

Four groups of operators.

Built-in general operators:

Operator	Meaning
+ - (unary)	positive, negative
+ - * /	arithmetic
++ --	list concatenation and subtraction
and / &&	strict / relaxed boolean and
or / ||	strict / relaxed boolean or
not / !	strict / relaxed boolean not
in not in	membership
@	module attribute
.. ..//	range creation
<>	binary concatenation
|>	pipeline
=~	text-based match

Many work in guards (see Patterns and guards). Special forms that cannot be overridden: ^ pin, . dot, = match, & capture, :: type. And these appear in the precedence table but only mean something in a construct: => (in %{}), when (guards), <- (for, with), \\ (default arguments).

Comparison operators

==, ===, !=, !==, <, >, <=, >=, all usable in guards. === differs from == only in being strict about integers and floats:

1 == 1.0    #=> true
1 === 1.0   #=> false

Precedence and associativity

Every operator Elixir can parse, from higher to lower precedence:

Higher rows bind tighter.

Two ternary operators: first..last//step (right) and %{map | key => value, ...} (none).

Associativity settles ties on the same row, and precedence settles different rows:

Same operator twice, or different operators together.

not left in right and !left in right currently parse as not(left in right), which contradicts the table. That is deprecated and warns. Write left not in right. A future major version will follow the table.

Custom and overridden operators

Elixir parses a fixed set of operators, so you can't invent new ones. But not every operator it parses is used: + and || are, <~> is valid but unused. Define one with def (or defp, defmacro) using operator syntax:

defmodule MyOperators do
  def a ~> b, do: max(a, b)
  def a <~ b, do: min(a, b)
end

import MyOperators
1 ~> 2   #=> 2
1 <~ 2   #=> 1

You must import the module to use them. Parsed but unused by default: |||, &&&, <<<, >>>, <<~, ~>>, <~, ~>, <~>, +++, ---, .... Bitwise uses &&&, <<<, >>> and ||| when imported.

The community discourages custom operators, which have no descriptive name, though some DSLs justify them. Replacing predefined operators such as + is extremely discouraged.