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use nqp;

# for proper R5RS semantics, run this once wrapping your main function
sub run_main($f) {
    nqp::continuationreset(nqp::null(), nqp::getattr($f<>, Code, Q[$!do]));
}

sub callcc($f) {
    # first get the current continuation
    nqp::continuationcontrol(1, nqp::null(), -> $dcont {
        my $scheme_cont := -> $val {
            # when the scheme continuation is invoked, we need to *replace*
            # the current continuation with this one
            nqp::continuationcontrol(1, nqp::null(), -> $c {
                nqp::continuationinvoke($dcont, { $val })
            });
        };
        nqp::continuationinvoke($dcont, { $f($scheme_cont) });
    });
}

callcc -> &f {
    for ^20 {
        if $_ == 15 {
            f();
        }
    }
}