Basic types

Source: Elixir guide, Basic types.

Integers, floats, atoms (booleans and nil among them) and strings. Lists and tuples come next.

Booleans and nil are atoms. Strings are binaries. Lists and tuples are covered next.

Numbers

1 + 2      #=> 3
5 * 5      #=> 25
10 / 2     #=> 5.0

/ always returns a float. For integer division and remainder use div/2 and rem/2:

div(10, 2)   #=> 5
rem(10, 3)   #=> 1

Binary, octal and hex literals are integers too (0b1010, 0o777, 0x1F). Floats are 64-bit and support scientific notation (1.0e-10). round/1 gives the closest integer, trunc/1 drops the fraction.

Booleans and nil

and, or and not are strict: the left side must be a boolean, or you get a BadBooleanError. They short-circuit, so the right side runs only when the left doesn't settle the answer.

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

false and raise("never raised")   #=> false

||, && and ! accept any value. Only false and nil are falsy. 0 and "" are truthy, unlike in some other languages.

Two falsy values. Everything else is truthy.

Rule of thumb: booleans in, use and / or / not. Anything else, use && / || / !.

Atoms

An atom is a constant whose value is its own name. Two atoms are equal when their names are equal. They usually stand for the state of an operation: :ok, :error.

true, false and nil are atoms, and the leading : is optional for them:

true == :true       #=> true
is_atom(false)      #=> true

Strings

Strings are UTF-8, in double quotes. <> concatenates (both sides must be strings). #{} interpolates any value that can become a string.

"hello " <> "world!"        #=> "hello world!"
"i am #{42} years old!"     #=> "i am 42 years old!"

Internally a string is a contiguous sequence of bytes, a binary. So bytes and characters can differ:

byte_size("hellö")       #=> 6
String.length("hellö")   #=> 5

"ö" is one grapheme but two bytes in UTF-8, so byte_size and String.length disagree.

Structural comparison

==, !=, <, <=, >, >= work across any types. 1 == 1.0 is true; use === to tell an integer from a float (1 === 1.0 is false).