mini template -- neither small nor inspiring

template.p6

my $template = q[
<title>%title</title>
<p>%body</p>
];

sub tmpl($template, &filter = -> $x { $x }, *%args) {
    $template.subst(:g, /'%'(\w+)/,
        -> $/ {
            %args.exists($0)
                ?? filter(%args{$0})
                !!  die("No value provided for '$1'")
        }
    );
}

say tmpl($template, &uc, title => 'HAI', body => 'foo.');