#!perl -w
use strict;

my $test;

$test = 2;
pr( 'no_zero' , $test , no_zero($test) ); # -> '1'
pr( 'a_zero'  , $test , a_zero($test)  ); # -> '1'

$test = 'pop';
pr( 'no_zero' , $test , no_zero($test) ); # -> 'undefined value' or ''
pr( 'a_zero'  , $test , a_zero($test)  ); # -> '0'

$test = undef;
pr( 'no_zero' , $test , no_zero($test) ); # -> ''
pr( 'a_zero'  , $test , a_zero($test)  ); # -> '0'


sub no_zero
{
  my $n = shift;

  my $re = qr/^ \d+ $/x;

  return
    #defined $n && $n =~ m/$re/
    scalar( defined $n && $n =~ m/$re/ )
  ;
}

sub a_zero
{ return no_zero( $_[0] ) || 0; }

sub pr
{ 
  my ($func , $val , $result) = @_;
  
  printf "%7s( '%s' ): '%s'\n" , ( $func , def($val) , def($result) );
  
  sub def 
  { my $v = shift;
    return ( (defined $v) ? $v : 'undefined value' );
  }
}


##</code><code>##

sub if_integer
{ my $i = shift;
 
  return defined $i && $i =~ m/^\d+$/;
}

##</code><code>##

  return defined $i && $i =~ m/^\d+$/ || 0;