Quoting Operators

Quoting operators and their various uses.

Introduction

Prog has a number of different quoting operators used to produce or represent different kinds of string data.

Table of Contents

• Introduction
• Table of Contents
• Basic Operators
  • Basic Strings
  • Quoted Identifiers
• Meta-Quoting
  • $e(), $enc()
  • $id()
  • $lang()
  • $q(), $quote()
  • $r(), $regex()
  • $s(), $split()
  • $x(), $expand()

Basic Operators

Basic Strings

Basic strings can be enclosed in double quotes ("") or single quotes (''):

my_string = "Hello, world!";
other_string = 'other';

A double-quoted string can contain a single-quoted expression; the expression is evaluated in string context and the result embedded in place of the expression. Likewise, a single-quoted string can contain a double-quoted expression:

phrase = "Hello, 'other_string' world!";
phrase = 'Hello, "other_string" world!';

An expression embedded in a string can contain quoted strings as well, provided that the type of quote is alternated:

hello = "Hello, ";
world = "world!";
result = "The length of 'hello''world' is 'length("'hello''world'")'.\n";

Quoted Identifiers

Any sequence of characters that does not contain a backquote (`) can be treated as an identifier by wrapping it in backquotes. This is often used for operator overloading:

`identifier with spaces` = 32;
def `+`(a as Point, b as Point) {
    return Point(a.x + b.x, a.y + b.y);
};

Note: to treat a single token as an identifier, it is possible to use \ rather than ``:

def \+(a as Point, b as Point) {};

Meta-Quoting Operators

Meta-quoting operators begin with a $ character followed by an identifier that determines their type, then a nonwhitespace character indicating the string delimiter. If the delimiter is a bracketing operator such as ( or <, the string is terminated by a corresponding ) or >. The string can contain the delimiter, but it must be escaped with \ if the operator would not be balanced. If the delimiter is a double or single quote, they cannot be nested as with ordinary strings. If the delimiter is any other character, the terminating delimiter is the same:

$e"UTF-8"
$i/foo/
$x(Foo = (foo))

Note that if string literals interpolate non-const expressions, they cease to be const. Consider interpolation the same as concatenation in this regard.

It is possible to create custom meta-quoting operators. See Operator Overloading.

Where short and long names are both given for quoting operators, the strict string pragma disables the short names in favour of the long ones.

$e(), $enc()

Returns an encoding type that, when applied to char, imbues the char with a specific character encoding.

$id()

Returns an identifier. This can be used to get around the restriction on backquoted identifiers containing backquotes. There is no $i(), because $id() is short enough.

$lang()

Returns a language type that, when applied to string, imbues the string with a specific locale. There is no $l(), to avoid ambiguity between the digit one and the letter L.

$q(), $quote()

Returns a string without performing interpolation.

$r(), $regex()

Returns a string that is treated as a regular expression, i.e., a regex string, which can be used with the matching operator (=~) to test for a match or as the left operand of an assignment to perform a replacement. See Pattern Matching.

$s(), $split()

Returns a tuple:string by splitting a string along whitespace, ignoring leading and trailing whitespace:

$s(foo bar baz) == ("foo", "bar", "baz");

$x(), $expand()

Returns a string, performing extended interpolation as with ordinary strings, but extending the concept of alternating quotes to nested bracketing delimiters ((), <>, etc.). $x cannot be used with any delimiters other than "", '', (), [], {}, and <>:

foo = $x[2 + 3 == [2 + 3]];
say = $x<The value of "foo" is "<foo>".>;