look how it generates code!

$ ./test-regex '^ [ <[a..d]>+ | <[b..e]>+ ] $' bcd
Concat[
  Anchor ('^') 
  Group[
    Alt[
      Quant ('greedy 1..Inf') [
        EnumCharList ('abcd') 
      ]
      Quant ('greedy 1..Inf') [
        EnumCharList ('bcde') 
      ]
    ]
  ]
  Anchor ('$') 
]

sub ($target, :$debug) {
    my $mfrom;
    my $cpos = 0;
    my $pos;
    my $rep;
    my $lastpos = $target.chars;
    my @gpad;   # TODO: PGE generates this one only when needed
    my @ustack; # 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');
                    break;
                }
                $mfrom = $pos = $cpos;
                local-branch('R');
            }
            when 'try_match_cont' {
                ++$cpos;
                goto('try_match');
            }
            when 'succeed' {
                return GGE::Match.new(:$target, :from($mfrom), :to($pos));
            }
            when 'fail' {
                local-return();
                if !@cstack {
                    return GGE::Match.new(:$target, :from(0), :to(-2));
                }
            } 
            # concat 
            when 'R' { # anchor ^ 
                if $pos == 0 { goto('R0'); break; }
                goto('fail'); 
            } 
            when 'R0' {
                push @ustack, $pos;
                local-branch('R2');
            }
            when 'R0_cont' {
                $pos = pop @ustack;
                goto('R3');
            } 
            when 'R2' { # quant greedy 1..Inf
                push @gpad, 0;
                local-branch('R2_repeat');
            }
            when 'R2_cont' {
                pop @gpad;
                goto('fail');
            }
            when 'R2_repeat' {
                $rep = @gpad[*-1];
                ++$rep;
                @gpad[*-1] = $rep;
                push @ustack, $pos;
                push @ustack, $rep;
                local-branch('R4');
            }
            when 'R2_repeat_cont' {
                $rep = pop @ustack;
                $pos = pop @ustack;
                --$rep;
                goto('R2_1');
            }
            when 'R2_1' {
                pop @gpad;
                push @ustack, $rep;
                local-branch('R1');
            }
            when 'R2_1_cont' {
                $rep = pop @ustack;
                push @gpad, $rep;
                goto('fail');
            }
        
            when 'R4' {
                if $pos >= $lastpos
                   || !defined 'abcd'.index($target.substr($pos, 1)) {
                    goto('fail');
                    break;
                }
                ++$pos;
                goto('R2_repeat');
            } 
            when 'R3' { # quant greedy 1..Inf
                push @gpad, 0;
                local-branch('R3_repeat');
            }
            when 'R3_cont' {
                pop @gpad;
                goto('fail');
            }
            when 'R3_repeat' {
                $rep = @gpad[*-1];
                ++$rep;
                @gpad[*-1] = $rep;
                push @ustack, $pos;
                push @ustack, $rep;
                local-branch('R5');
            }
            when 'R3_repeat_cont' {
                $rep = pop @ustack;
                $pos = pop @ustack;
                --$rep;
                goto('R3_1');
            }
            when 'R3_1' {
                pop @gpad;
                push @ustack, $rep;
                local-branch('R1');
            }
            when 'R3_1_cont' {
                $rep = pop @ustack;
                push @gpad, $rep;
                goto('fail');
            }
        
            when 'R5' {
                if $pos >= $lastpos
                   || !defined 'bcde'.index($target.substr($pos, 1)) {
                    goto('fail');
                    break;
                }
                ++$pos;
                goto('R3_repeat');
            } 
            when 'R1' { # anchor $ 
                if $pos == $lastpos { goto('succeed'); break; }
                goto('fail'); 
            } 
            default {
                die "Don't know a label {@cstack[*-1]}";
            }
        }
    }
} 

mob: <bcd @ 0>