p6.p6

use MONKEY;

role Iterable2 {
    method flat2(Iterable:D:) {
        Seq.new(class :: does Iterator {
            has Iterator $!source;
            has Iterator $!nested;

            method new(\source) {
                nqp::p6bindattrinvres(nqp::create(self),self,'$!source',source)
            }

            my constant NO_RESULT_YET = nqp::create(Mu);
            method pull-one() is raw {
                my $result := NO_RESULT_YET;
                my $got;
                nqp::while(
                  nqp::eqaddr($result, NO_RESULT_YET),
                  nqp::if(
                    $!nested,
                    nqp::if(
                      nqp::eqaddr(($got := $!nested.pull-one),IterationEnd),
                      ($!nested := Iterator),
                      ($result := $got)
                    ),
                    nqp::if(
                      nqp::istype(($got := $!source.pull-one),Iterable)
                        && nqp::not_i(nqp::iscont($got)),
                      ($!nested := $got.flat.iterator),
                      ($result := $got)
                    )
                  )
                );
                $result
            }

            method push-all($target --> IterationEnd) {
                state $foo = 0;
                my $got;
                my $iterator := $!nested || $!source;
                dd [[$iterator.pull-one], [$iterator.pull-one], [$iterator.pull-one], $iterator.pull-one];
                exit;
                nqp::until(
                       nqp::eqaddr(($got := $iterator.pull-one), IterationEnd)
                    && nqp::eqaddr($iterator, $!source),
                    nqp::stmts(
                        ($foo++),
                        nqp::if(
                            nqp::istype($got, IterationEnd),
                            nqp::stmts(($iterator := $!source)),
                            nqp::if(
                                   nqp::istype($got,Iterable)
                                && nqp::not_i(nqp::iscont($got)),
                                nqp::stmts(
                                    (dd $foo), ($iterator := $got.flat.iterator)
                                ),
                                $target.push($got),
                            ),
                        )
                    )
                );
            }
        }.new(self.iterator))
    }
}

augment class List does Iterable2 {}

my @a := List.from-iterator: <a b c d e f g>[0..2, 3, 4].flat2.iterator;
say @a.Bool;
say @a.elems;
dd @a;