[oak perl] until loop(s)

[Steve Fink]

Sandy Santra wrote:
> I'm learning (struggling with) "until" loops today.  I want an "until" 
> control structure that "breaks out" when a condition is fulfilled.
> 
> Can anyone find the problem in the below loop?  (It never breaks out.)  
> Thanks.
> 
> use strict;
> print "Can you create world peace in five tries?  Type a solution 
> below:\n";
> my $number;
> until (my $counter == 5)
> 
> {
>         while ($number=<STDIN>)
>         {
>         $counter=$counter+1;
>         print "Counter is now $counter.\n";
>         print "You still have a few tries left.\n";
>         }
> }
> print "You failed!  The human race is doomed!\n";

The problem is scoping. The 'my' inside of the counter makes this code 
similar to:

   until (something) {
     my $counter;
     $counter = $counter + 1;
   }

so every time through the loop, it resets $counter to undef.

There's no equivalent code to insert in place of "something", because I 
think it is using the correct $counter variable. It's really closer to

   until (0) {
     my $counter;
     last if $counter == 5;
     $counter = $counter + 1;
   }

But if you change your code to

   my $counter;
   until ($counter == 5) {
     ...$counter = $counter + 1...
   }

it will work.

I would have expected your original to work, honestly. But I also never 
stick 'my' into the middle of expressions, other than a few limited 
cases. Makes my head hurt too much.