cue: implement custom escape delimiters
Aka raw strings.
This approach to raw strings is a verbatim copy of raw
strings as introduced in Swift 5.
The API of ResumeInterpolation has been changed as it was
otherwise too awkward.
See https://github.com/apple/swift-evolution/blob/master/proposals/0200-raw-string-escaping.md.
Change-Id: Ib25b749cb1573fc2b4072c90878c3c63ebb5fd38
diff --git a/doc/ref/spec.md b/doc/ref/spec.md
index dd1df4d..9153fa3 100644
--- a/doc/ref/spec.md
+++ b/doc/ref/spec.md
@@ -356,10 +356,15 @@
String literals may only be valid UTF-8.
Byte sequences may contain any sequence of bytes.
-Several backslash escapes allow arbitrary values to be encoded as ASCII text
-in interpreted strings.
+Several escape sequences allow arbitrary values to be encoded as ASCII text.
+An escape sequence starts with an _escape delimiter_, which is `\` by default.
+The escape delimiter may be altered to be `\` plus a fixed number of
+hash symbols `#`
+by padding the start and end of a string or byte sequence literal
+with this number of hash symbols.
+
There are four ways to represent the integer value as a numeric constant: `\x`
-followed by exactly two hexadecimal digits; \u followed by exactly four
+followed by exactly two hexadecimal digits; `\u` followed by exactly four
hexadecimal digits; `\U` followed by exactly eight hexadecimal digits, and a
plain backslash `\` followed by exactly three octal digits.
In each case the value of the literal is the value represented by the
@@ -373,7 +378,7 @@
Hexadecimal escapes satisfy this condition by construction.
The escapes `\u` and `\U` represent Unicode code points so within them
some values are illegal, in particular those above `0x10FFFF`.
-Surrogate halves are allowed to be compatible with JSON,
+Surrogate halves are allowed,
but are translated into their non-surrogate equivalent internally.
The three-digit octal (`\nnn`) and two-digit hexadecimal (`\xnn`) escapes
@@ -384,8 +389,6 @@
the two bytes `0xc3 0xbf` of the UTF-8
encoding of character `U+00FF`.
-After a backslash, certain single-character escapes represent special values:
-
```
\a U+0007 alert or bell
\b U+0008 backspace
@@ -406,24 +409,35 @@
All other sequences starting with a backslash are illegal inside literals.
```
-escaped_char = `\` ( "a" | "b" | "f" | "n" | "r" | "t" | "v" | `\` | "'" | `"` ) .
-unicode_value = unicode_char | little_u_value | big_u_value | escaped_char .
+escaped_char = `\` { `#` } ( "a" | "b" | "f" | "n" | "r" | "t" | "v" | `\` | "'" | `"` ) .
byte_value = octal_byte_value | hex_byte_value .
octal_byte_value = `\` octal_digit octal_digit octal_digit .
hex_byte_value = `\` "x" hex_digit hex_digit .
little_u_value = `\` "u" hex_digit hex_digit hex_digit hex_digit .
big_u_value = `\` "U" hex_digit hex_digit hex_digit hex_digit
hex_digit hex_digit hex_digit hex_digit .
+unicode_value = unicode_char | little_u_value | big_u_value | escaped_char .
+interpolation = "\(" Expression ")" .
-string_lit = interpreted_string_lit |
- interpreted_bytes_lit |
- multiline_lit .
+string_lit = simple_string_lit |
+ multiline_string_lit |
+ simple_bytes_lit |
+ multiline_bytes_lit |
+ `#` string_lit `#` .
-interpolation = "\(" Expression ")" .
-interpreted_string_lit = `"` { unicode_value | interpolation } `"` .
-interpreted_bytes_lit = `"` { unicode_value | interpolation | byte_value } `"` .
+simple_string_lit = `"` { unicode_value | interpolation } `"` .
+simple_bytes_lit = `"` { unicode_value | interpolation | byte_value } `"` .
+multiline_string_lit = `"""` newline
+ { unicode_value | interpolation | newline }
+ newline `"""` .
+multiline_bytes_lit = "'''" newline
+ { unicode_value | interpolation | byte_value | newline }
+ newline "'''" .
```
+Carriage return characters (`\r`) inside string literals are discarded from
+the raw string value.
+
```
'a\000\xab'
'\007'
@@ -438,6 +452,10 @@
"\xff\u00FF"
"\uD800" // illegal: surrogate half (TODO: probably should allow)
"\U00110000" // illegal: invalid Unicode code point
+
+#"This is not an \(interpolation)"#
+#"This is an \#(interpolation)"#
+#"The sequence "\U0001F604" renders as \#U0001F604."#
```
These examples all represent the same string:
@@ -455,13 +473,11 @@
combining form involving an accent and a letter, the result will appear as two
code points if placed in a string literal.
-Each of the interpreted string variants have a multiline equivalent.
-Multiline interpreted strings are like their single-line equivalent,
+Strings and byte sequences have a multiline equivalent.
+Multiline strings are like their single-line equivalent,
but allow newline characters.
-Carriage return characters (`\r`) inside raw string literals are discarded from
-the raw string value.
-Multiline interpreted strings and byte sequences respectively start with
+Multiline strings and byte sequences respectively start with
a triple double quote (`"""`) or triple single quote (`'''`),
immediately followed by a newline, which is discarded from the string contents.
The string is closed by a matching triple quote, which must be by itself
@@ -473,16 +489,6 @@
To include it is suffices to escape one of the quotes.
```
-multiline_lit = multiline_string_lit | multiline_bytes_lit .
-multiline_string_lit = `"""` newline
- { unicode_char | interpolation | newline }
- newline `"""` .
-multiline_bytes_lit = "'''" newline
- { unicode_char | interpolation | newline | byte_value }
- newline "'''" .
-```
-
-```
"""
lily:
out of the water
@@ -923,7 +929,7 @@
FieldDecl = Label { Label } ":" Expression .
AliasDecl = Label "=" Expression .
-Label = identifier | interpreted_string_lit | TemplateLabel .
+Label = identifier | simple_string_lit | TemplateLabel .
TemplateLabel = "<" identifier ">" .
Tag = "#" identifier [ ":" json_string ] .
```
@@ -1851,7 +1857,7 @@
_Field comprehensions_ follow a `Field` with a clause sequence, where the
label and value of the field are evaluated for each iteration.
-The label must be an identifier or interpreted_string_lit, where the
+The label must be an identifier or simple_string_lit, where the
later may be a string interpolation that refers to the identifiers defined
in the clauses.
Values of iterations that map to the same label unify into a single field.
