Kernel.tap

You're seeing just the macro tap, go back to Kernel module for more information.

tap(value, fun)

(macro) (since 1.12.0)

Pipes value to the given fun and returns the value itself.

Useful for running synchronous side effects in a pipeline.

iex> tap(1, fn x -> x + 1 end)
1

Most commonly, this is used in pipelines. For example, let's suppose you want to inspect part of a data structure. You could write:

%{a: 1}
|> Map.update!(:a, & &1 + 2)
|> tap(&IO.inspect(&1.a))
|> Map.update!(:a, & &1 * 2)