Kernel.tap

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

tap(value, fun)

View Source (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.

Examples

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)