Trace Failure

traceTest.p6

# The script below runs fine with out trace, but with trace
# I get the following error:
#
# Type Block does not support associative indexing.
#   in block <unit> at traceTest.p6 line 16

use trace;

sub proc(*@cmd) {
    # Takes a terminal command and starts a new async process
    # Returns the process, channel with stdout/stderr, and promise
    my $proc = Proc::Async.new(|@cmd, :w);
    my $out = Channel.new;
    $proc.Supply.tap( -> $str { $out.send($str) } );
    my $promise = $proc.start;
    return {proc => $proc, out => $out, prom => $promise};
}

my $test = proc('echo', 'hello world');
my $output;
until $output ~~ "hello world\n" {
    $output = $test{'out'}.poll;
}
say $output;