You can name a capture if you think that's an improvement over numbered captures (see the two lines with comments):

my regex line {
    ^^
    (\w+) :my $s; <?{ $s = %sigils{$0} }>
    \h+
    $s $<foo>=\N* $s # Note the foo bit here ...
    $$
}

is  ('bang !one!' ~~ m/<line>/)<line><foo>, 'one', 'is   bang!one'; # 
+... and here
[download]

Another tweak is to drop one level of hash keys by using a grammar (again, see the two lines with comments):

grammar g {
    regex TOP { # drop 'my'; name 'TOP' to simplify .parse call in `is
+` test
    ^^
    (\w+) :my $s;  <?{ $s = %sigils{$0} }>
    \h+
    $s $<foo>=\N* $s
    $$
    }
}

is  g.parse('bang !one!')<foo>,     'one', 'is   bang!one'; # calling 
+.parse method on grammar defaults to starting with rule (regex) named
+ 'TOP'
[download]