Elixir Koans - Enum.take with Negative Numbers Prints Ascii

Question

I was running through some Elixir Koans and came across the following:

  think "taking some items the other way" do
    numbers = 1..10
    assert Enum.take(numbers, -2) == __?
  end

After spending a lot of time on this I finally looked at it in iex and I get:

'\t\n'

After more experimentation:

Enum.take(numbers, -4) == '\a\b\t\n'
Enum.take(numbers, -5) == [6, 7, 8, 9, 10]

Why does this print out ascii sometimes and the list I'm expecting other times? What happens at 7?

Related: http://stackoverflow.com/questions/25978873/avoid-converting-numbers-to-characters-in-erlang — aronisstav, Jan 27 '16 at 10:03

Josh Petitt · Accepted Answer · 2016-01-26T14:17:39.337

2

From Elixir FAQ

Pretty-printing of lists is done by using Erlang's native function. It is designed to print lists as strings when all elements of the list are valid ASCII codes.

At 7 you have BEL '\a' (the a is for 'alert' AFIAK)

At 6 you have ACK which apparently doesn't have a printable representation

edited Jan 26 '16 at 14:17

answered Jan 26 '16 at 14:12

Josh Petitt

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So why does adding a zero or anything string at the end of the list make it print correctly? – ChrisBarthol Jan 26 '16 at 14:53
Because then it isn't a list of printable ASCII codes anymore. – Alexey Romanov Jan 26 '16 at 14:57
Ah right since the last two I would be printing are not valid. – ChrisBarthol Jan 26 '16 at 15:01

Elixir Koans - Enum.take with Negative Numbers Prints Ascii

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