Why does IO.inspect print escape characters?

Questions / Help
1

Hello

I have a newbie question. Why does IO.inspect give the following result?

IO.inspect [[6,9], [7,9], [8,9], [9,9]]

Output:
[[6, 9], ‘\a\t’, ‘\b\t’, ‘\t\t’]

What is up with the escape characters?

1 Like
2

Anytime you are curious about something like that, put i in front of it in the shell:

iex(1)> i '7,9'
Term
  '7,9'
Data type
  List
Description
  This is a list of integers that is printed as a sequence of characters
  delimited by single quotes because all the integers in it represent valid
  ASCII characters. Conventionally, such lists of integers are referred to
  as "charlists" (more precisely, a charlist is a list of Unicode codepoints,
  and ASCII is a subset of Unicode).
Raw representation
  [55, 44, 57]
Reference modules
  List
Implemented protocols
  IEx.Info, Collectable, Enumerable, Inspect, List.Chars, String.Chars

I.E. a list of integers is a charlist. :slight_smile:

2 Likes
3

Thank you for a quick reply! :slight_smile:

4

General Elixir Newbie Advice: Always use double quotes when you use strings! You only use single quotes basically when interfacing with erlang code which uses charlists for its string representation system.

5

But why is the first list “list of numbers” [6,9] not escaped, and the rest are? I find this very odd…

6

If integer is “non ASCII”, it will be shown as it is. Otherwise, the character, that is under this number in ASCII table. Check this answer on SO.

6 Likes
7

Thank you

8

Bumping this excellent Noob question.

This is something confuses many new to Elixir. The Inspect protocol for lists (which is what displays something in iex, defaults to a charlist if all the elements of the list are printable characters, including printable control characters like \t \r \n, etc.

If you are working in iex, this can be a pain if you’re looking at an integer list that just happens to have all printable characters. If you have this issue in iex, try using i on the list, or add a non printing integer to the list as shown below.

iex(1)> 'test'
'test'

iex(11)> 'test' ++ [0]
[116, 101, 115, 116, 0]

iex(8)> [9, 13, 48, 50]
'\t\r02'

iex(9)> i '\t\r02'
Term
  '\t\r02'
Data type
  List
Description
  This is a list of integers that is printed as a sequence of characters
  delimited by single quotes because all the integers in it represent valid
  ASCII characters. Conventionally, such lists of integers are referred to as
  "charlists" (more precisely, a charlist is a list of Unicode codepoints,
  and ASCII is a subset of Unicode).
Raw representation
  [9, 13, 48, 50]
Reference modules
  List
Implemented protocols
  IEx.Info, Inspect, String.Chars, List.Chars, Collectable, Enumerable

iex(10)> [0, 9, 13, 48, 50]
[0, 9, 13, 48, 50]

iex(13)> '\t\r02' == [9, 13, 48, 50]
true
4 Likes
9

Thanks :slight_smile:

1 Like