sub halts {
    my $machine = shift;
    my $input = shift;
    is_whatever_nullary(
       qq{
          run_turing_equivalent("\Q$machine\E", "\Q$input\E");
          sub whatever() {};
       }
    )
}

##</code><code>##

BEGIN {
    if(  0.5 < rand()  ) {
        eval "sub whatever() { }; 1" or die $@;
    } else {
        eval "sub whatever { }; 1" or die $@;
    }
}
whatever  / 25 ; # / ; die "this dies!";

##</code><code>##

 > perl -MO=Deparse above.pl
# ...
whatever / 25;
- syntax OK

 > perl -MO=Deparse above.pl
# ...
whatever(/ 25 ; # /);
die 'this dies!';
- syntax OK