In Regexes §

See primary documentation in context for Subrules

Just like you can put pieces of code into subroutines, you can also put pieces of regex into named rules.

Raku highlighting

my regex line { \N*\n }
if "abc\ndef" ~~ /<line> def/ {
    say "First line: ", $<line>.chomp;      # OUTPUT: «First line: abc␤» 
}

A named regex can be declared with my regex named-regex { body here }, and called with <named-regex>. At the same time, calling a named regex installs a named capture with the same name.

To give the capture a different name from the regex, use the syntax <capture-name=named-regex>. If no capture is desired, a leading dot or ampersand will suppress it: <.named-regex> if it is a method declared in the same class or grammar, <&named-regex> for a regex declared in the same lexical context.

Here's more complete code for parsing ini files:

Raku highlighting

my regex header { \s* '[' (\w+) ']' \h* \n+ }
my regex identifier  { \w+ }
my regex kvpair { \s* <key=identifier> '=' <value=identifier> \n+ }
my regex section {
    <header>
    <kvpair>*
}
 
my $contents = q:to/EOI/; 
    [passwords]
        jack=password1
        joy=muchmoresecure123
    [quotas]
        jack=123
        joy=42
EOI
 
my %config;
if $contents ~~ /<section>*/ {
    for $<section>.list -> $section {
        my %section;
        for $section<kvpair>.list -> $p {
            %section{ $p<key> } = ~$p<value>;
        }
        %config{ $section<header>[0] } = %section;
    }
}
say %config.raku;
 
# OUTPUT: «{:passwords(${:jack("password1"), :joy("muchmoresecure123")}), 
#           :quotas(${:jack("123"), :joy("42")})}»

Named regexes can and should be grouped in grammars. A list of predefined subrules is here.

In Regexes§

In Regexes §