code generation in GGE

$ ./test-regex '<[a..b]> | <[b..e]>' c
Alt[
  EnumCharList ('ab') 
  EnumCharList ('bcde') 
]

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));
                }
            } 
            when 'R' { # alt R0, R1
                push @ustack, $pos;
                local-branch('R0');
            }
            when 'R_cont' {
                $pos = pop @ustack;
                goto('R1');
            } 
            when 'R0' {
                if $pos >= $lastpos
                   || !defined 'ab'.index($target.substr($pos, 1)) {
                    goto('fail');
                    break;
                }
                ++$pos;
                goto('succeed');
            } 
            when 'R1' {
                if $pos >= $lastpos
                   || !defined 'bcde'.index($target.substr($pos, 1)) {
                    goto('fail');
                    break;
                }
                ++$pos;
                goto('succeed');
            } 
            default {
                die "Don't know a label {@cstack[*-1]}";
            }
        }
    }
} 

mob: <c @ 0>