fold: /TIMES|PLUS|DIV|MINUS/(NUM($n), $op, NUM($m))
=> {
$op = $op->{attr};
$n->{attr} = eval "$n->{attr} $op $m->{attr}";
$_[0] = $NUM[0]; # return true value
}
zero_times_whatever: TIMES(NUM($x), ., .) and { $x->{attr} == 0 } => { $_[0] = $NUM }
whatever_times_zero: TIMES(., ., NUM($x)) and { $x->{attr} == 0 } => { $_[0] = $NUM }
/* rules related with times */
times_zero = zero_times_whatever whatever_times_zero;
{
=head1 SYNOPSIS
Compile it with
eyapp -m 'Calc' Rule9.yp
treereg -o T.pm -p 'R::' -m T Transform4
to execute, run C<foldand0rule9_4.pl>
=cut
}