Ranges represent a sequence of one or many, ascending or descending, consecutive integers.

Ranges can be either increasing (first <= last) or decreasing (first > last). Ranges are also always inclusive.

A range is represented internally as a struct. However, the most common form of creating and matching on ranges is via the ../2 macro, auto-imported from Kernel:

iex> range = 1..3
1..3
iex> first..last = range
iex> first
1
iex> last
3

A range implements the Enumerable protocol, which means functions in the Enum module can be used to work with ranges:

iex> range = 1..10
1..10
iex> Enum.reduce(range, 0, fn i, acc -> i * i + acc end)
385
iex> Enum.count(range)
10
iex> Enum.member?(range, 11)
false
iex> Enum.member?(range, 8)
true

Such function calls are efficient memory-wise no matter the size of the range. The implementation of the Enumerable protocol uses logic based solely on the endpoints and does not materialize the whole list of integers.