use Term::ReadLine;
my $term = Term::ReadLine->new('Simple Perl calc');
my $prompt = "Enter code: ";
my $OUT = $term->OUT || \*STDOUT;
while ( defined ($_ = $term->readline($prompt)) ) {
  my $res = eval("package allowed_subs; $_");
  warn $@ if $@;
  print $OUT $res, "\n" unless $@;
  $term->addhistory($_) if /\S/;
}
  
package allowed_subs;
 
sub ab {
  `xmessage "@_"`       # Pop-Up input  (linux only)
}