Quoting constructs
The Q lang
Strings are usually represented in Raku code using some form of quoting
construct. The most minimalistic of these is Q
, usable via the shortcut
「…」
, or via Q
followed by any pair of delimiters surrounding your
text, including many
Unicode pairs.
Most of the time, though, the most you'll need is
'…'
or "…"
,
described in more detail in the following sections.
For information about quoting as applied in regexes, see the regular expression documentation.
Literal strings: Q
Q[A literal string]
「More plainly.」
Q^Almost any non-word character can be a delimiter!^
Q「「Delimiters can be repeated/nested if they are adjacent.」」
Q⦅Quoting with fancy unicode pairs⦆
Delimiters can be nested, but in the plain Q
form, backslash escapes
aren't allowed. In other words, basic Q
strings are as literal as
possible.
Some delimiters are not allowed immediately after Q
, q
, or qq
. Any
characters that are allowed in identifiers are
not allowed to be used, since in such a case, the quoting construct together
with such characters are interpreted as an identifier. In addition, ( )
is
not allowed because that is interpreted as a function call. If you still wish
to use those characters as delimiters, separate them from Q
, q
, or qq
with a space. Please note that some natural languages use a left delimiting
quote on the right side of a string. Q
will not support those as it relies
on unicode properties to tell left and right delimiters apart.
Q'this will not work!'
Q(this won't work either!)
The examples above will produce an error. However, this will work
Q (this is fine, because of space after Q)
Q 'and so is this'
Q<Make sure you <match> opening and closing delimiters>
Q{This is still a closing curly brace → \}
These examples produce:
this is fine, because of space after Q
and so is this
Make sure you <match> opening and closing delimiters
This is still a closing curly brace → \
The behavior of quoting constructs can be modified with adverbs, as explained in detail in later sections.
Short | Long | Meaning |
:x | :exec | Execute as command and return results |
:w | :words | Split result on words (no quote protection) |
:ww | :quotewords | Split result on words (with quote protection) |
:q | :single | Interpolate \\, \qq[...] and escaping the delimiter with \ |
:double | Interpolate with :s, :a, :h, :f, :c, :b | |
:s | :scalar | Interpolate $ vars |
:a | :array | Interpolate @ vars (when followed by postcircumfix) |
:h | :hash | Interpolate % vars (when followed by postcircumfix) |
:f | :function | Interpolate & calls |
:c | :closure | Interpolate {...} expressions |
:b | :backslash | Enable backslash escapes (\n, \qq, \$foo, etc) |
:to | :heredoc | Parse result as heredoc terminator |
:v | :val | Convert to allomorph if possible |
These adverbs can be used together with Q
, so that it will interpolate
even if the quoting operator does not:
my %þ = :is-mighty;
say Q "Þor %þ<>"; # OUTPUT: «Þor %þ<>»
say Q:h"Þor %þ<>"; # OUTPUT: «Þor is-mighty True»
%þ = :42foo, :33bar;
say Q:h:c "Þor %þ<> → { [+] %þ.values}"; # OUTPUT: «Þor bar 33foo 42 → 75»
my @þ= <33 44>; say Q:a "Array contains @þ[]"; # OUTPUT: «Array contains 33 44»
say Q:v<33> + 3; # OUTPUT: «36»
By default, and as shown, Q
quotes directly without any kind of
transformation of the quoted string. The adverbs will modify its behavior,
converting, for instance, the string into an allomorph (with the :v
adverb)
or allowing interpolation of hashes (via :h
) or {}
code sections (via
:c
). Arrays and hashes must be followed by a postcircumfix; that is, the
sigiled identifier will not interpolate, but followed by an indexing, decont
operator or a method call with parentheses, it will:
my @þ= <33 44>;
say Q:a "Array contains @þ.elems()"; # OUTPUT: «Array contains 2»
The same code without the parentheses will simply not interpolate, absent the post-circumfix operator.
Escaping: q
'Very plain';
q[This back\slash stays];
q[This back\\slash stays]; # Identical output
q{This is not a closing curly brace → \}, but this is → };
Q :q $There are no backslashes here, only lots of \$\$\$!$;
'(Just kidding. There\'s no money in that string)';
'No $interpolation {here}!';
Q:q!Just a literal "\n" here!;
The q
form allows for escaping characters that would otherwise end the
string using a backslash. The backslash itself can be escaped, too, as in
the third example above. The usual form is '…'
or q
followed by a
delimiter, but it's also available as an adverb on Q
, as in the fifth and
last example above.
These examples produce:
Very plain
This back\slash stays
This back\slash stays
This is not a closing curly brace → } but this is →
There are no backslashes here, only lots of $$$!
(Just kidding. There's no money in that string)
No $interpolation {here}!
Just a literal "\n" here
The \qq[...]
escape sequence enables
qq interpolation for a portion
of the string. Using this escape sequence is handy when you have HTML markup
in your strings, to avoid interpretation of angle brackets as hash keys:
my $var = 'foo';
say '<code>$var</code> is <var>\qq[$var.uc()]</var>';
# OUTPUT: «<code>$var</code> is <var>FOO</var>»
Interpolation: qq
my $color = 'blue';
say "My favorite color is $color!"; # OUTPUT: «My favorite color is blue!»
The qq
form – usually written using double quotes – allows for
interpolation of backslash escape sequences (like q:backslash
), all sigiled
variables (like q:scalar:array:hash:function
), and any code inside {...}
(like q:closure
).
Interpolating variables
Inside a qq
-quoted string, you can use variables with a sigil to trigger
interpolation of the variable's value. Variables with the $
sigil are
interpolated whenever the occur (unless escaped); that's why, in the example
above, "$color"
became blue
.
Variables with other sigils, however, only trigger interpolation when you follow
the variable with the appropriate postfix ([]
for Arrays, <>
, for Hashes,
&
for Subs). This allows you to write expressions like
"[email protected]"
without interpolating the @raku
variable.
To interpolate an Array (or other Positional variable),
append a []
to the variable name:
my @neighbors = "Felix", "Danielle", "Lucinda";
say "@neighbors[] and I try our best to coexist peacefully."
# OUTPUT: «Felix Danielle Lucinda and I try our best to coexist peacefully.»
Alternatively, rather than using []
, you can interpolate the Array by
following it with a method call with parentheses after the method name. Thus the
following code will work:
say "@neighbors.join(', ') and I try our best to coexist peacefully."
# OUTPUT: «Felix, Danielle, Lucinda and I try our best to coexist peacefully.»
However, "@example.com"
produces @example.com
.
To call a subroutine, use the &
-sigil and follow the subroutine name with parentheses.
say "uc 'word'"; # OUTPUT: «uc 'word'»
say "&uc 'word'"; # OUTPUT: «&uc 'word'»
say "&uc('word')"; # OUTPUT: «WORD»
# OUTPUT: «abcDEFghi»
To interpolate a Hash (or other Associative variable), use
the <>
postcircumfix operator.
my %h = :1st; say "abc%h<st>ghi";
# OUTPUT: «abc1ghi»
The way qq
interpolates variables is the same as
q:scalar:array:hash:function
. You can use these adverbs (or their short
forms, q:s:a:h:f
) to interpolate variables without enabling other qq
interpolations.
Interpolating closures
Another feature of qq
is the ability to interpolate Raku code from
within the string, using curly braces:
my ($x, $y, $z) = 4, 3.5, 3;
say "This room is {$x}m by {$y}m by {$z}m."; # OUTPUT: «This room is 4m by 3.5m by 3m.»
say "Therefore its volume should be { $x * $y * $z }m³!"; # OUTPUT: «Therefore its volume should be 42m³!»
This provides the same functionality as the q:closure
/q:c
quoting form.
Interpolating escape codes
The qq
quoting form also interpolates backslash escape sequences. Several of
these print invisible/whitespace ASCII control codes or whitespace characters:
Sequence | Hex Value | Character | Reference URL |
\0 | \x0000 | Nul | https://util.unicode.org/UnicodeJsps/character.jsp?a=0000 |
\a | \x0007 | Bel | https://util.unicode.org/UnicodeJsps/character.jsp?a=0007 |
\b | \x0008 | Backspace | https://util.unicode.org/UnicodeJsps/character.jsp?a=0008 |
\e | \x001B | Esc | https://util.unicode.org/UnicodeJsps/character.jsp?a=001B |
\f | \x000C | Form Feed | https://util.unicode.org/UnicodeJsps/character.jsp?a=000C |
\n | \x000A | Newline | https://util.unicode.org/UnicodeJsps/character.jsp?a=000A |
\r | \x000D | Carriage Return | https://util.unicode.org/UnicodeJsps/character.jsp?a=000D |
\t | \x0009 | Tab | https://util.unicode.org/UnicodeJsps/character.jsp?a=0009 |
qq
also supports two multi-character escape sequences: \x
and \c
. You
can use \x
or \x[]
with the hex-code of a Unicode character or a list of
characters:
my $s = "I \x2665 Raku!";
say $s;
# OUTPUT: «I ♥ Raku!»
$s = "I really \x[2661,2665,2764,1f495] Raku!";
say $s;
# OUTPUT: «I really ♡♥❤💕 Raku!»
You can also create a Unicode character with \c
and that character's
unicode name
, named sequences
or name alias:
my $s = "Camelia \c[BROKEN HEART] my \c[HEAVY BLACK HEART]!";
say $s;
# OUTPUT: «Camelia 💔 my ❤!»
See the description of \c[] on the Unicode documentation page for more details.
qq
provides the same interpolation of escape sequences as that
provided by q:backslash
/q:b
.
preventing interpolation and handling missing values
You can prevent any undesired interpolation in a
qq
-quoted string by escaping the sigil or other initial character:
say "The \$color variable contains the value '$color'"; # OUTPUT: «The $color variable contains the value 'blue'»
Interpolation of undefined values will raise a control exception that can be caught in the current block with CONTROL.
sub niler {Nil};
my Str $a = niler;
say("$a.html", "sometext");
say "alive"; # this line is dead code
CONTROL { .die };
Word quoting: qw
qw|! @ # $ % ^ & * \| < > | eqv '! @ # $ % ^ & * | < >'.words.list;
q:w { [ ] \{ \} } eqv ('[', ']', '{', '}');
Q:w | [ ] { } | eqv ('[', ']', '{', '}');
The :w
form, usually written as qw
, splits the string into
"words". In this context, words are defined as sequences of non-whitespace
characters separated by whitespace. The q:w
and qw
forms inherit the
interpolation and escape semantics of the q
and single quote string
delimiters, whereas Qw
and Q:w
inherit the non-escaping semantics of
the Q
quoter.
This form is used in preference to using many quotation marks and commas for lists of strings. For example, where you could write:
my @directions = 'left', 'right,', 'up', 'down';
It's easier to write and to read this:
my @directions = qw|left right up down|;
Word quoting: < >
|Syntax,< > word quote
say <a b c> eqv ('a', 'b', 'c'); # OUTPUT: «True»
say <a b 42> eqv ('a', 'b', '42'); # OUTPUT: «False», the 42 became an IntStr allomorph
say < 42 > ~~ Int; # OUTPUT: «True»
say < 42 > ~~ Str; # OUTPUT: «True»
The angle brackets quoting is like qw
, but with extra feature that lets you
construct allomorphs or literals
of certain numbers:
say <42 4/2 1e6 1+1i abc>.raku;
# OUTPUT: «(IntStr.new(42, "42"), RatStr.new(2.0, "4/2"), NumStr.new(1000000e0, "1e6"), ComplexStr.new(<1+1i>, "1+1i"), "abc")»
To construct a Rat or Complex literal, use angle brackets around the number, without any extra spaces:
say <42/10>.^name; # OUTPUT: «Rat»
say <1+42i>.^name; # OUTPUT: «Complex»
say < 42/10 >.^name; # OUTPUT: «RatStr»
say < 1+42i >.^name; # OUTPUT: «ComplexStr»
Compared to 42/10
and 1+42i
, there's no division (or addition) operation
involved. This is useful for literals in routine signatures, for example:
sub close-enough-π (<355/113>) {
say "Your π is close enough!"
}
close-enough-π 710/226; # OUTPUT: «Your π is close enough!»
# WRONG: can't do this, since it's a division operation
sub compilation-failure (355/113) {}
Word quoting with quote protection: qww
The qw
form of word quoting will treat quote characters literally, leaving
them in the resulting words:
say qw{"a b" c}.raku; # OUTPUT: «("\"a", "b\"", "c")»
Using the qww
variant allows you to use quote characters for embedding strings
in the word quoting structure:
say qww{"a b" c}.raku; # OUTPUT: «("a b", "c")»
Other kinds of quotes are also supported with their usual semantics:
my $one = 'here';
my $other = 'there';
say qww{ ’this and that’ “$one or $other” 「infinity and beyond」 }.raku;
# OUTPUT: «("this and that", "here or there", "infinity and beyond")»
The delimiters of embedded strings are always considered word splitters:
say qww{'alpha'beta'gamma' 'delta'"epsilon"}.raku; # OUTPUT: «("alpha", "beta", "gamma", "delta", "epsilon")»
Word quoting with interpolation: qqw
The qw
form of word quoting doesn't interpolate variables:
my $a = 42; say qw{$a b c}; # OUTPUT: «$a b c»
Thus, if you wish for variables to be interpolated within the quoted string,
you need to use the qqw
variant:
my $a = 42;
my @list = qqw{$a b c};
say @list; # OUTPUT: «[42 b c]»
Note that variable interpolation happens before word splitting:
my $a = "a b";
my @list = qqw{$a c};
.say for @list; # OUTPUT: «abc»
<<Word quoting with interpolation and quote protection: qqww|Syntax,qqww>>
The qqw
form of word quoting will treat quote characters literally,
leaving them in the resulting words:
my $a = 42; say qqw{"$a b" c}.raku; # OUTPUT: «("\"42", "b\"", "c")»
Using the qqww
variant allows you to use quote characters for embedding strings
in the word quoting structure:
my $a = 42; say qqww{"$a b" c}.raku; # OUTPUT: «("42 b", "c")»
The delimiters of embedded strings are always considered word splitters:
say qqww{'alpha'beta'gamma' 'delta'"epsilon"}.raku; # OUTPUT: «("alpha", "beta", "gamma", "delta", "epsilon")»
Unlike the qqw
form, interpolation also always splits (except for interpolation that takes place in an embedded string):
my $time = "now";
$_ = 'ni';
my @list = qqww<$time$time {6*7}{7*6} "$_$_">;
.say for @list; # OUTPUT: «nownow4242nini»
Quote protection happens before interpolation, and interpolation happens before word splitting, so quotes coming from inside interpolated variables are just literal quote characters:
my $a = "1 2";
say qqww{"$a" $a}.raku; # OUTPUT: «("1 2", "1", "2")»
my $b = "1 \"2 3\"";
say qqww{"$b" $b}.raku; # OUTPUT: «("1 \"2 3\"", "1", "\"2", "3\"")»
<<Word quoting with interpolation and quote protection: « »>;Syntax,« »>>>
This style of quoting is like qqww
, but with the added benefit of
constructing allomorphs (making it
functionally equivalent to qq:ww:v). The
ASCII equivalent to « »
are double angle brackets << >>
.
# Allomorph Construction
my $a = 42; say « $a b c ».raku; # OUTPUT: «(IntStr.new(42, "42"), "b", "c")»
my $a = 42; say << $a b c >>.raku; # OUTPUT: «(IntStr.new(42, "42"), "b", "c")»
# Quote Protection
my $a = 42; say « "$a b" c ».raku; # OUTPUT: «("42 b", "c")»
my $a = 42; say << "$a b" c >>.raku; # OUTPUT: «("42 b", "c")»
Shell quoting: qx
To run a string as an external program, not only is it possible to pass the
string to the shell
or run
functions but one can also perform shell
quoting. There are some subtleties to consider, however. qx
quotes
don't interpolate variables. Thus
my $world = "there";
say qx{echo "hello $world"}
prints simply hello
. Nevertheless, if you have declared an environment
variable before calling raku
, this will be available within qx
, for
instance
WORLD="there" raku
> say qx{echo "hello $WORLD"}
will now print hello there
.
The result of calling qx
is returned, so this information can be assigned
to a variable for later use:
my $output = qx{echo "hello!"};
say $output; # OUTPUT: «hello!»
See also shell, run and Proc::Async for other ways to execute external commands.
Shell quoting with interpolation: qqx
If one wishes to use the content of a Raku variable within an external
command, then the qqx
shell quoting construct should be used:
my $world = "there";
say qqx{echo "hello $world"}; # OUTPUT: «hello there»
Again, the output of the external command can be kept in a variable:
my $word = "cool";
my $option = "-i";
my $file = "/usr/share/dict/words";
my $output = qqx{grep $option $word $file};
# runs the command: grep -i cool /usr/share/dict/words
say $output; # OUTPUT: «CooleyCooley'sCoolidgeCoolidge'scool...»
Be aware of the content of the Raku variable used within an external command; malicious content can be used to execute arbitrary code. See qqx traps
See also run and Proc::Async for better ways to execute external commands.
Heredocs: :to
A convenient way to write a multi-line string literal is by using a heredoc, which lets you choose the delimiter yourself:
say q:to/END/;
Here is
some multi-line
string
END
The contents of the heredoc always begin on the next line, so you can (and should) finish the line.
my $escaped = my-escaping-function(q:to/TERMINATOR/, language => 'html');
Here are the contents of the heredoc.
Potentially multiple lines.
TERMINATOR
If the terminator is indented, that amount of indention is removed from the string literals. Therefore this heredoc
say q:to/END/;
Here is
some multi line
string
END
produces this output:
Here is
some multi line
string
Heredocs include the newline from before the terminator.
To allow interpolation of variables use the qq
form, but you will then have
to escape metacharacters \{
as well as $
if it is not the sigil for a
defined variable. For example:
my $f = 'db.7.3.8';
my $s = qq:to/END/;
option \{
file "$f";
};
END
say $s;
would produce:
option {
file "db.7.3.8";
};
Some other situations to pay attention to are innocent-looking ones where the text looks like a Raku expression. For example, the following generates an error:
my $title = 'USAFA Class of 1965';
say qq:to/HERE/;
<a href='https://usafa-1965.org'>$title</a>
HERE
# Output:
Type Str does not support associative indexing.
in block <unit> at here.raku line 2
The angle bracket to the right of '$title' makes it look like a hash index to Raku when it is actually a Str variable, hence the error message. One solution is to enclose the scalar with curly braces which is one way to enter an expression in any interpolating quoting construct:
say qq:to/HERE/;
<a href='https://usafa-1965.org'>{$title}</a>
HERE
Another option is to escape the `<` character to avoid it being parsed as the beginning of an indexing operator:
say qq:to/HERE/;
<a href='https://usafa-1965.org'>$title\</a>
HERE
Because a heredoc can be very long but is still interpreted by Raku as a single line, finding the source of an error can sometimes be difficult. One crude way to debug the error is by starting with the first visible line in the code and treating is as a heredoc with that line only. Then, until you get an error, add each line in turn. (Creating a Raku program to do that is left as an exercise for the reader.)
You can begin multiple Heredocs in the same line. If you do so, the second heredoc will not start until after the first heredoc has ended.
my ($first, $second) = qq:to/END1/, qq:to/END2/;
FIRST
MULTILINE
STRING
END1
SECOND
MULTILINE
STRING
END2
say $first; # OUTPUT: «FIRSTMULTILINESTRING»
say $second; # OUTPUT: «SECONDMULTILINESTRING»
Unquoting
Literal strings permit interpolation of embedded quoting constructs by using the escape sequences such as these:
my $animal="quaggas";
say 'These animals look like \qq[$animal]'; # OUTPUT: «These animals look like quaggas»
say 'These animals are \qqw[$animal or zebras]'; # OUTPUT: «These animals are quaggas or zebras»
In this example, \qq
will do double-quoting interpolation, and \qqw
word
quoting with interpolation. Escaping any other quoting construct as above will
act in the same way, allowing interpolation in literal strings.