Elixir - How to format the output of a List on Iex

Question

I'm doing a small Cli program with Ecto and when I do a query for some results I get a list and in the time that I've been learning Elixir something that I can't do right in the Terminal is to format the output of a function that returns a list.

When I run Repo.all(from u in Entry, select: u.title) I get a list like this:

["test title", "second title"] and I want to format that output to be like:

*****
test title
*****
second title

A division per item in the list but I don't know how to exactly do it or an efficent way of doing so. I've tried list comprehensions but well... it returns a list. Tried piping Enum.map/2 to IO.puts/1 with no result so now I require some help :-)

Answer 1

I'd use Enum.map_join/3 :

iex(1)> ["test title", "second title"] |>
...(1)> Enum.map_join("\n", &["*****\n", &1]) |>
...(1)> IO.puts
*****
test title
*****
second title

Answer 2

You can try this

Repo.all(from u in Entry, select: u.title) |> 
Enum.reduce([], fn item, acc -> 
  ["********", item | acc]
end) |> Enum.reverse |> Enum.join("\n") |> IO.puts

Or a more reusable approach

iex(8)> display = fn list -> list |> Enum.reduce([], fn item, acc -> ["**********", item | acc] end) |> Enum.reverse |> Enum.join("\n") |> IO.puts end
#Function<6.54118792/1 in :erl_eval.expr/5>
iex(9)> ["test title", "second title"] |> display.()                                                                    test title
**********
second title
**********
:ok
iex(10)> ~w(one two three four) |> display.()
one
**********
two
**********
three
**********
four
**********
:ok
iex(11)>

I often use the anoyn function approach in iex. can create little functions like that and reuse them without needing to define a module.

Here I added the display function in to my .iex.exs file. An ran it from a new iex session

Interactive Elixir (1.4.2) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> ~w(one two) |> display.()
one
**********
two
**********
:ok
iex(2)>

EDIT

If you wanted a real generic solution, you could override the inspect protocol in iex. However, this could affect your program if it uses inspect anywhere.

ex(7)> defimpl Inspect, for: List do
...(7)> def inspect(list, _opt \\ []), do: Enum.map_join(list, "\n", &(["*******\n", &1]))
...(7)> end
warning: redefining module Inspect.List (current version defined in memory)
  iex:7

{:module, Inspect.List,
 <<70, 79, 82, 49, 0, 0, 7, 184, 66, 69, 65, 77, 69, 120, 68, 99, 0, 0, 0, 242,
   131, 104, 2, 100, 0, 14, 101, 108, 105, 120, 105, 114, 95, 100, 111, 99, 115,
   95, 118, 49, 108, 0, 0, 0, 4, 104, 2, ...>>, {:__impl__, 1}}
iex(8)> ["Test one", "Test two"]
*******
Test one
*******
Test two
iex(9)>