use strict;
use constant DEBUG => 1;

# many lines of code here

&assert($val, $var1, $var2) if DEBUG;

# many lines of code here

sub assert() {
   my $test = shift;
   my (@vars) = @_;

   # test $test for condition
   # if test condition is true 
   # do something with @vars (usually dump them)

   print "would you like to abort: ";
   my $ans = <STDIN>;
   exit if $ans =~ m/y/i;

}