sub filter (&@) {
    (wantarray ?
        sub { @_ } :
        sub { join '', @_ }
    )->(
        map { local $_ = $_; $_[0]->(); $_ }  @_[1 .. $#_]
    );
}

##</code><code>##

sub filter (&@) {
    my ($func, @out) = @_;
    $func->() for @out;
    wantarray ? @out : join '', @out;
}