The do…end block is one way of grouping expressions and passing them to other code. They are used in module and named function definitions, control structures…any place in Elixir where code needs to be handled as an entity.
However, do…end is not actually the underlying syntax. The actual syntax looks like this:
| | def double(n), do: n * 2 |
You can pass multiple lines to do: by grouping them with parentheses.
| | def greet(greeting, name), do: ( |
| | IO.puts greeting |
| | IO.puts "How're you doing, #{name}?" |
| | ) |
The do…end form is just a lump of syntactic sugar—during compilation it is turned into the do: form. (And the do: form itself is nothing special; it is simply a term in a keyword list.) Typically people use the do: syntax for single-line blocks, and do…end for multiline ones.
This means our times example would probably be written as follows:
| | defmodule Times do |
| | def double(n), do: n * 2 |
| | end |
We could even write it as
| | defmodule Times, do: (def double(n), do: n*2) |
(but please don’t).