Psuedo Code:
use Cool::PrePostModule;
###
# some precondition documented here
# some postcondition documented here
###
sub functionname
{
   # get all yer args here
   &setPrecondtion('something == somethingelse');
   &setPostcondition('thisthing == thatthing');

   &checkPrecondition('somethingelse') or die 'I cant verify precondition';

   #yadayadayada

   &checkPostcondition('thatthing') or die 'I cant verify postcondition';
}