Operators

The Pipe Operator

The Pipe Operator |> takes the result of an expression on the left and feeds it as the first parameter to a function on the right.

expression |> function

Use the Pipe Operator to chain expressions together and to visually document the flow of a series of functions.

Consider the following:

Oven.bake(Ingredients.Mix([:flour, :cocoa, :sugar, :milk, :eggs, :butter]), :temperature)

In the example, Oven.bake comes before Ingredients.mix, but it is executed last. Also, it may not be obvious that :temperature is a parameter of Oven.bake

Rewriting this example using the Pipe Operator:

[:flour, :cocoa, :sugar, :milk, :eggs, :butter]
|> Ingredients.mix
|> Oven.bake(:temperature)

gives the same result, but the order of execution is clearer. Furthermore, it is clear that :temperature is a parameter to the Oven.bake call.

Note that when using the Pipe Operator, the first parameter for each function is relocated to before the Pipe Operator, and so the function being called appears to have one fewer parameter. For instance:

Enum.each([1, 2, 3], &(&1+1)) # produces [2, 3, 4]

is the same as:

[1, 2, 3]
|> Enum.each(&(&1+1))

Pipe operator and parentheses

Parentheses are needed to avoid ambiguity:

foo 1 |> bar 2 |> baz 3

Should be written as:

foo(1) |> bar(2) |> baz(3)

Boolean operators

There are two kinds of boolean operators in Elixir:

• boolean operators (they expect either true or false as their first argument)

  x or y # true if x is true, otherwise y

  x and y # false if x is false, otherwise y

  not x # false if x is true, otherwise true

All of booleans operators will raise ArgumentError if first argument won’t be strictly boolean value, which means only true or false (nil is not boolean).

iex(1)> false and 1 # return false
iex(2)> false or 1 # return 1 
iex(3)> nil and 1 # raise (ArgumentError) argument error: nil

• relaxed boolean operators (work with any type, everything that neither false nor nil is considered as true)

  x || y # x if x is true, otherwise y

  x && y # y if x is true, otherwise false

  !x # false if x is true, otherwise true

Operator || will always return first argument if it’s truthy (Elixir treats everything except nil and false to be true in comparisions), otherwise will return second one.

iex(1)> 1 || 3 # return 1, because 1 is truthy
iex(2)> false || 3 # return 3
iex(3)> 3 || false # return 3
iex(4)> false || nil # return nil
iex(5)> nil || false # return false

Operator && will always return second argument if it’s truthy. Otherwise will return respectively to the arguments, false or nil.

iex(1)> 1 && 3 # return 3, first argument is truthy
iex(2)> false && 3 # return false
iex(3)> 3 && false # return false 
iex(4)> 3 && nil # return nil
iex(5)> false && nil # return false
iex(6)> nil && false # return nil

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

Operator ! will return boolean value of negation of current term:

iex(1)> !2 # return false
iex(2)> !false # return true
iex(3)> !"Test" # return false
iex(4)> !nil # return true

Simple way to get boolean value of selected term is to simply double this operator:

iex(1)> !!true # return true
iex(2)> !!"Test" # return true
iex(3)> !!nil # return false
iex(4)> !!false # return false

Comparison operators

Equality:

• value equality x == y (1 == 1.0 # true)
• value inequality x == y (1 != 1.0 # false)
• strict equality x === y (1 === 1.0 # false)
• strict inequality x === y (1 !== 1.0 # true)

Comparison:

• x > y
• x >= y
• x < y
• x <= y

If types are compatible, comparison uses natural ordering. Otherwise there is general types comparison rule:

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

Join operators

You can join (concatenate) binaries (including strings) and lists:

iex(1)> [1, 2, 3] ++ [4, 5]
[1, 2, 3, 4, 5]

iex(2)> [1, 2, 3, 4, 5] -- [1, 3]
[2, 4, 5]

iex(3)> "qwe" <> "rty"
"qwerty"

‘In’ operator

in operator allows you to check whether a list or a range includes an item:

iex(4)> 1 in [1, 2, 3, 4]
true

iex(5)> 0 in (1..5)
false