Re^2: A way to avoid repeated conditional loops

You can't rely on readline returning EOF or errors more than once. Fix:

OUTER: {
   for (;;) {
      defined( my $_ = <$fh> ) or last OUTER;
      if (/alpha/) {
         f();
         last;
      } else {
         g();
      }
   }

   while (<$fh>) {
      g();
   }
}
[download]

Update: The remainder of this post is wrong.

You can get rid of the duplicate g() by making the loops bottom tested.

OUTER: {
   defined( my $_ = <$fh> ) or last OUTER;

   for (;;) {
      if (/alpha/) {
         f();
         last;
      }

      defined( $_ = <$fh> ) or last OUTER;
   }

   for (;;) {
      g();

      defined( $_ = <$fh> ) or last OUTER;
   }
}
[download]

You can squish it down a bit:

LOOP: {
   defined( my $_ = <$fh> ) or last;

   if (/alpha/) {
      f();
      redo;
   }

   for (;;) {
      g();
      defined( $_ = <$fh> ) or last;
   }
}
[download]

Look at that, g() is not even duplicated anymore!!

Comment on Re^2: A way to avoid repeated conditional loops Select or Download Code

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Re^3: A way to avoid repeated conditional loops by jffry (Hermit) on Aug 24, 2011 at 19:39 UTC
Why is your `for` loop idiom better than AR's or JavaFan's `while` loop statements above?	[reply]
Re^4: A way to avoid repeated conditional loops by ikegami (Patriarch) on Aug 24, 2011 at 20:36 UTC
I already pointed out that AR's version is wrong. You can't rely on readline returning EOF or errors more than once. I thought mine was better than JavaFan's because it lead to the elimination of the duplicate "g()", but that turned out to be a mistake (as per my earlier update). I still prefer mine over JavaFan's, though. Since mine flows from top to bottom, it requires less skipping around to follow the code.	[reply]
Re^5: A way to avoid repeated conditional loops by jffry (Hermit) on Aug 24, 2011 at 21:46 UTC
Ah! Now I see what you're saying. Using AR's code, suppose the file is empty, then the very first `while (<FILE>)` will return `EOF`, then the code flows to the second `while (<FILE>)`. There, even though the file pointer is at the end of the file, the `<>` operator won't return an `EOF` a second time. And the code in that second `while` loop will get executed when it should not. Thinking of it this way, I can now see how both yours and JavaFan's code avoid that trap. Thanks.	[reply]
Re^3: A way to avoid repeated conditional loops by Deus Ex (Scribe) on Aug 25, 2011 at 13:41 UTC
The squished version is really cool :) It looks I got my solution! Many thanks ikegami!	[reply]
Re^4: A way to avoid repeated conditional loops by ikegami (Patriarch) on Aug 25, 2011 at 17:45 UTC
That version doesn't do anything until it reaches the first alpha. Is that really what you want?	[reply]
Re^5: A way to avoid repeated conditional loops by Deus Ex (Scribe) on Aug 29, 2011 at 03:44 UTC
You're right. Was naming the first block of code you wrote as "the squished version". Of course it was not :) Actually I've been realizing that there's no way other than using either a regex to test on the evaluated current line or a flag variable. At this point it seems to me the second approach might be the most efficient in computational terms. Many thanks for your help :)	[reply]