IP.localhost

You're seeing just the function localhost, go back to IP module for more information.

Specs

localhost(:v4) :: v4()
localhost(:v6) :: v6()

returns the canonical ip address of localhost. Defaults to ipv4.

iex> IP.localhost()
{127, 0, 0, 1}

iex> IP.localhost(:v6)
{0, 0, 0, 0, 0, 0, 0, 1}