output.txt

$ perl6 foo.p6 
Not consumed yet
touched in: 
	 -> sink-all (SETTING::src/core/Any-iterable-methods.pm:459)
	 -> sink (SETTING::src/core/Seq.pm:195)
	 -> <anon> (foo.p6:2)
	 -> CALL-ME (SETTING::src/core/Routine.pm:85)
	 -> map (SETTING::src/core/Any-iterable-methods.pm:17)
	 -> map (SETTING::src/core/Any-iterable-methods.pm:11)
	 -> foo (foo.p6:11)
	 -> <unit> (foo.p6:1)

ABCAlready consumed
touched in: 
	 -> sink-all (SETTING::src/core/Any-iterable-methods.pm:459)
	 -> sink (SETTING::src/core/Seq.pm:195)
	 -> <anon> (foo.p6:2)
	 -> CALL-ME (SETTING::src/core/Routine.pm:85)
	 -> map (SETTING::src/core/Any-iterable-methods.pm:17)
	 -> foo (foo.p6:11)
	 -> <unit> (foo.p6:1)

Not consumed yet
touched in: 
	 -> sink-all (SETTING::src/core/Any-iterable-methods.pm:459)
	 -> sink (SETTING::src/core/Seq.pm:195)
	 -> <anon> (foo.p6:2)
	 -> CALL-ME (SETTING::src/core/Routine.pm:85)
	 -> map (SETTING::src/core/Any-iterable-methods.pm:17)
	 -> is-runtime (SETTING::src/core/Backtrace.pm:321)
	 -> anon (SETTING::src/core/Exception.pm:339)
	 -> print_exception (SETTING::src/core/Exception.pm:327)
	 -> <anon> (SETTING::src/core/Exception.pm:421)

p6.p6

use nqp;
Seq.^lookup("iterator").wrap: method (|) {
    say nqp::defined(nqp::getattr(self, Seq, '$!iter'))
        ?? 'Not consumed yet' !! 'Already consumed';
    say "touched in: ";
    for 3..20 { try say "\t -> {.name || <anon>} ({.file}:{.line})" with callframe($_).code }
    put();
    nextsame;
};

sub foo {
    my $s := <a b c>.map: *.uc;
    .print for $s;
    .print for $s;
}()