Elixir Language Lists List Comprehensions
Example
Elixir doesn't have loops. Instead of them for lists there are great Enum and List modules, but there are also List Comprehensions.
List Comprehensions can be useful to:
- create new lists
iex(1)> for value <- [1, 2, 3], do: value + 1
[2, 3, 4]
- filtering lists, using
guardexpressions but you use them withoutwhenkeyword.
iex(2)> odd? = fn x -> rem(x, 2) == 1 end
iex(3)> for value <- [1, 2, 3], odd?.(value), do: value
[1, 3]
- create custom map, using
intokeyword:
iex(4)> for value <- [1, 2, 3], into: %{}, do: {value, value + 1}
%{1 => 2, 2=>3, 3 => 4}
Combined example
iex(5)> for value <- [1, 2, 3], odd?.(value), into: %{}, do: {value, value * value}
%{1 => 1, 3 => 9}
Summary
List Comprehensions:
- uses
for..dosyntax with additional guards after commas andintokeyword when returning other structure than lists ie. map. - in other cases return new lists
- doesn't support accumulators
- can't stop processing when certain condition is met
guardstatements have to be first in order afterforand beforedoorintosymbols. Order of symbols doesn't matter
According to these constraints List Comprehensions are limited only for simple usage. In more advanced cases using functions from Enum and List modules would be the best idea.
