Interpolation and escaping in sigils

Besides lowercase sigils, Elixir supports uppercase sigils to deal with escaping characters and interpolation. While both ~s and ~S will return strings, the former allows escape codes and interpolation while the latter does not:

iex> ~s(String with escape codes \x26 #{"inter" <> "polation"})
"String with escape codes & interpolation"
iex> ~S(String without escape codes \x26 without #{interpolation})
"String without escape codes \\x26 without \#{interpolation}"

The following escape codes can be used in strings and char lists:

• \" – double quote
• \' – single quote
• \\ – single backslash
• \a – bell/alert
• \b – backspace
• \d - delete
• \e - escape
• \f - form feed
• \n – newline
• \r – carriage return
• \s – space
• \t – tab
• \v – vertical tab
• \0 - null byte
• \xDD - character with hexadecimal representation DD (e.g., \x13)
• \x{D...} - character with hexadecimal representation with one or more hexadecimal digits (e.g., \x{abc13})

Sigils also support heredocs, that is, triple double- or single-quotes as separators:

iex> ~s"""
...> this is
...> a heredoc string
...> """

The most common use case for heredoc sigils is when writing documentation. For example, writing escape characters in documentation would soon become error prone because of the need to double-escape some characters:

@doc """
Converts double-quotes to single-quotes.

## Examples

    iex> convert("\\\"foo\\\"")
    "'foo'"

"""
def convert(...)

By using ~S, this problem can be avoided altogether:

@doc ~S"""
Converts double-quotes to single-quotes.

## Examples

    iex> convert("\"foo\"")
    "'foo'"

"""
def convert(...)