perl6 Colored match, some regex interpolation works and some don't; color code inconsistent

Question

I have some long lines and I want to highlight the matches with colors that I want. One function uses substitution, and the other function uses recursion. Some works and some don't; I am looking for a consistent way to interpolating into regex. Thank you very much !!!

sub colorMatch ($aStr, $aRegex, $aColor) {
    my $colorOff = '\e[0m';
    my $a =$aStr.subst(/(<{$aRegex}>)/, $aColor ~ "# $/ #" ~ $colorOff, :g);
    # not working, $/ not interpolating corresponding matches, all Nil
    say $a;
}

colorMatch("a-12-b-3-c-4-def-567", '\d+', '\e[1;31m');
colorMatch("a-12-b-3-c-4-def-567", '<alpha>+', '\e[1;31m');
say "\e[1;31m" ~ " color1 " ~ "\e[0m" ~ 
    "\e[1;36m" ~ " color2 " ~ "\e[0m";

sub colorMatch2 ($aStr, $aRegex, $colorNumber) {
    my $colorOff = "\e[0m";
    if $aStr.chars > 0 {
    my $x1 = ($aStr ~~ m/<{$aRegex}>/);
    my $x2 = $x1.prematch;
    my $x3 = $x1.Str;
    my $x4 = $x1.postmatch;
    return ($x2 ~ "\e[1;{$colorNumber}m" ~ $x3 ~ $colorOff)
        ~ colorMatch2($x4, $aRegex, $colorNumber);
    }
}

say colorMatch2("a-12-b-3-c-4-def-567", '\d+', 31); # works, red color
say colorMatch2("a-12-b-3-c-4-def-567", '567', 36); # works, green color
say colorMatch2("a-12-b-3-c-4-def-567", '\w+', 31); # works, red color
say colorMatch2("a-12-b-3-c-4-def-567", '[a..z]+', 31); # fails with [] and ..
say colorMatch2("a-12-b-3-c-4-def-567", "<alpha>+", 31); # fails with <>


Use of Nil in string context
  in sub colorMatch at colorMatch.pl line 4
a-\e[1;31m#  #\e[0m-b-\e[1;31m#  #\e[0m-c-\e[1;31m#  #\e[0m-def-\e[1;31m#  #\e[0m

# seems to do substitution, but $/ is empty and color not shown;

Use of Nil in string context
  in sub colorMatch at colorMatch.pl line 4
\e[1;31m#  #\e[0m-12-\e[1;31m#  #\e[0m-3-\e[1;31m#  #\e[0m-4-\e[1;31m#  #\e[0m-567

# seems to do substitution, but $/ is empty and color not shown;

 color1  color2 # both colors work and shown as expected, 
 # color1 red and color 2 green; why inconsistent with above???

a-12-b-3-c-4-def-567 # works, red color
a-12-b-3-c-4-def-567 # works, green color
a-12-b-3-c-4-def-567 # works, red color
No such method 'prematch' for invocant of type 'Bool'
  in sub colorMatch2 at colorMatch.pl line 17
  in block <unit> at colorMatch.pl line 28

Answer 1

It's not an interpolation problem. The syntax for character classes and ranges is a little different. You need:

'text' ~~ / <[a..z]>+ /

As for your other error about calling prematch() on a bool, the result is False because in the final recursion level, it doesn't match anymore. You need to check the result before assuming it matched.

Finally, for "Use of Nil in string context", it's because you're using Str.subst, and like most function calls in most languages, the arguments are evaluated before the function begins. You're using $/ in an argument, but it's not yet set because the function's body hasn't even started to execute. The s/match/replacement/ operator does not suffer this difficulty, so I suggest you change your code to:

$aStr ~~ s:g/(<$aRegex>)/$aColor# $/ #$colorOff/;

(Or for better readability:)

$aStr ~~ s:g {(<$aRegex>)} = "$aColor# $/ #$colorOff";

This assumes you've made $aRegex into a regex rather than a string. Also, since the new code modifies $aStr, you need to change $aStr to $aStr is copy in the function signature.