captures and GGE

$ ./test-regex '[(.)$0]+' bookkeeper
Quant ('greedy 1..Inf') [
  Group[
    Concat[
      CGroup[
        CCShortcut ('.') 
      ]
      Scalar ('$0') 
    ]
  ]
]

sub ($target, :$debug) {
    my $mob = GGE::Match.new(:$target);
    my $mfrom;
    my $cpos = 0;
    my $pos;
    my $rep;
    my $lastpos = $target.chars;
    my $cutmark;
    my @gpad;             # TODO: PGE generates this one only when needed
    my @ustack;           # TODO: PGE generates this one only when needed
    my $captscope = $mob; # TODO: PGE generates this one only when needed
    my $captob;           # TODO: PGE generates this one only when needed
    my @cstack = 'try_match';
    my &goto = -> $label { @cstack[*-1] = $label };
    my &local-branch = -> $label {
        @cstack[*-1] ~= '_cont';
        @cstack.push($label)
    };
    my &local-return = -> { @cstack.pop };
    loop {
        given @cstack[*-1] {
            when 'try_match' {
                if $cpos > $lastpos { goto('fail_rule'); break; }
                $mfrom = $pos = $cpos;
                $cutmark = 0;
                local-branch('R');
            }
            when 'try_match_cont' {
                if $cutmark <= -2 { goto('fail_cut'); break; }
                ++$cpos;
                goto('try_match');
            }
            when 'fail_rule' {
                # $cutmark = -2 # XXX: Not needed yet
                goto('fail_cut');
            }
            when 'fail_cut' {
                $mob.from = 0;
                $mob.to = -2;
                return $mob;
            }
            when 'succeed' {
                $mob.from = $mfrom;
                $mob.to = $pos;
                return $mob;
            }
            when 'fail' {
                local-return();
            } 
            when 'R' { # quant 1..Inf (greedy) greedy/none
                push @gpad, 0;
                local-branch('R_repeat');
            }
            when 'R_cont' {
                pop @gpad;
                ### if $cutmark != 0 { goto('fail'); break; }
                ### $cutmark = 0;
                goto('fail');
            }
            when 'R_repeat' {
                $rep = @gpad[*-1];
                ### if $rep >= Inf { goto('R_1'); break; }
                ++$rep;
                @gpad[*-1] = $rep;
                push @ustack, $pos;
                push @ustack, $rep;
                local-branch('R1');
            }
            when 'R_repeat_cont' {
                $rep = pop @ustack;
                $pos = pop @ustack;
                if $cutmark != 0 { goto('fail'); break; }
                --$rep;
                goto('R_1');
            }
            when 'R_1' {
                if $rep < 1 { goto('fail'); break; }
                pop @gpad;
                push @ustack, $rep;
                local-branch('succeed');
            }
            when 'R_1_cont' {
                $rep = pop @ustack;
                push @gpad, $rep;
                if $cutmark != 0 { goto('fail'); break; }
                ### $cutmark = 0;
                goto('fail');
            } 
            # concat 
            when 'R1' { # capture
                if defined $captscope[0] {
                    goto('R1_cgen');
                    break;
                }
                $captscope[0] = [];
                local-branch('R1_cgen');
            }
            when 'R1_cont' {
                $captscope[0] = undef;
                goto('fail');
            }
            when 'R1_cgen' { 
                goto('R1_1');
            }
            when 'R1_1' {
                $captob = $captscope.new($captscope);
                $captob.from = $pos; # XXX: PGE uses .pos here somehow.
                push @gpad, $captscope;
                push @gpad, $captob;
                $captscope = $captob;
                local-branch('R3');
            }
            when 'R1_1_cont' {
                $captob = pop @gpad;
                $captscope = pop @gpad;
                ### if $cutmark != ... { goto('fail'); break; }
                ### $cutmark = 0;
                goto('fail');
            }
            when 'R1_close' {
                push @ustack, $captscope;
                $captob = pop @gpad;
                $captscope = pop @gpad;
                $captob.to = $pos;
                $captscope[0].push($captob);
                push @ustack, $captob;
                local-branch('R2');
            }
            when 'R1_close_cont' {
                $captob = pop @ustack;
                $captscope[0].pop();
                push @gpad, $captscope;
                push @gpad, $captob;
                $captscope = pop @ustack;
                goto('fail');
            } 
            when 'R3' { # ccshortcut .
                if $pos >= $lastpos || False {
                    goto('fail');
                    break;
                }
                ++$pos;
                goto('R1_close');
            } 
            when 'R2' { # scalar 0
                my $capture = $mob[0];
                if $capture ~~ Array {
                    $capture = $capture[*-1];
                }
                my $length = $capture.chars;
                if $pos + $length > $lastpos
                   || $target.substr($pos, $length) ne $capture {
                    goto('fail');
                    break;
                }
                $pos += $length;
                goto('R_repeat');
            } 
            default {
                die "No such label: {@cstack[*-1]}";
            }
        }
    }
} 

mob: <ookkee @ 1> 
mob 0 0: <o @ 1> 
mob 0 1: <k @ 3> 
mob 0 2: <e @ 5>