[swift-evolution] Alternate proposal for multi-line string literial

[Steve K. Chiu]

Hi,

I am new to swift-evolution list, here is my draft proposal for the
multi-line string literal problem.
The idea had been discussed in the list before, but it seems there are no
real solution to many of the string literal problem.
Let's first define what are the problem with string literal:

1. should be able to disable escape char

2. or better, able to replace escape char with user defined char

3. should be able to write multi-line string literal, and is copy-paste
friendly

4. for multi-line string, should be  able to remove first and last newline
char, so user can write string in block

5. for multi-line string, should be  able to remove leading indent, or
remove all indent

6. for multi-line string, should be  able to replace newline with user
defined string ("\r\n", "\r", "\r", or simply " ")

7. should be able to add feature over time, without breaking existing code

My proposal to the above problem is to introduce new 'process instruction'
(not sure how to call it), in the following form:

#string(options) "text"

for example:

#string(escape: nil) "^\d+"

#string(escape: "$", end: "<EOF>") "
   $(username),
   Is it 1358 yet?
<EOF>"

It is possible to add many options list above, and you can add more options
over time without breaking code.

#string(
    escape: Character? = "\\",
    end: String? = nil,
    skipEnclosureNewline: Bool = true,
    skipLeadingIndent: Bool = true,
    skipAllIndent: Bool = false,
    newline: String? = nil
)

for 1. & 2., escape option to replace escape char, pass nil will disable
escape.

for 3., end option for end-of-string mark, pass nil will disable multi-line
processing.

for 4., skipEnclosureNewline will skip newline if it is the first or last
char of the string.

for 5., skipLeadingIndent will skip leading indent, leading indent is the
leading white-spaces of first line of multi-line string.

for 5., skipAllIndent will skip all indent, this will override
skipLeadingIndent.

for 6., newline option to replace newline char in multi-line string, pass
nil will disable the replacement (as-is in the source).

But there are one problem remain, as you can see, the #string with options
will become very long; I don't think it is a pleasure to use such
expression except for one time literal. To fix the problem, I propose yet
another process instruction:

#let #rex = #string(escape: nil)
#let #mail = #string(escape: "$", end: "<EOF>")

Now you can write the string as:

#rex "^\d+"

#mail "
   $(username),
   Is it 1358 yet?
<EOF>"

#let should be able to be used with other # process instruction as well,
for example, #available, among other things.

What do you think?
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