# perl program illustrating closures and a kind of objects

sub mktoggle
{
   my $v = $_[0];
   if ($v>1 || $v<0) {die "what planet are you from?"}
   sub
   {
      $v = ($v+1) % 2;
      $v
   }
}


$t1 = mktoggle(0);
$t2 = mktoggle(1);

print $t1->(), "\n";  # changes state
print $t2->(), "\n"; 



# Clearly, t1 and t2 are functions that carry STATE information.  They 
# share the SAME SOURCE CODE, but they are clearly different entities!
# Their behavior is more like those of methods as opposed to functions.

# now expand - there's other information we may want concerning the local
# state of these functions - we may want to see the current value of v 
# without changing it, or we may wish to reset it to zero.  In other words,
# we want three operations to be associated with the local state that was
# created:

# toggle: toggles value and returns new value
# getval: returns value without toggling
# reset:  reset value to zero

sub mktginstance
{
   my $v = $_[0];
   if ($v>1 || $v<0) {die "what planet are you from?"}
   
   my $toggle = sub   
      {
        $v = ($v+1) % 2;  
        $v
      };

   my $getval = sub { $v };
  
   my $reset = sub { $v = 0; };

   # Now for the INTERFACE function:

   sub 
   {
      my $request = $_[0];
      if ($request eq "getval") {return $getval->();}
      if ($request eq "toggle") {return $toggle->();}
      if ($request eq "reset")  {return $reset->(); }
      else {"request denied"}
   }

} # mktginstance


$t1 = mktginstance(0);
$t2 = mktginstance(1);

print "------------\n";
print $t1->(getval), "\n";
$t1->(toggle);
print $t1->(getval), "\n";
$t1->(reset);
print $t1->(getval), "\n";