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Re^4: last in a do while loop (for (;;))

by ikegami (Patriarch)
on Nov 03, 2006 at 21:38 UTC ( [id://582174]=note: print w/replies, xml ) Need Help??


in reply to Re^3: last in a do while loop
in thread last in a do while loop

There's one significant advantage (from the reader's point of view) to while (1):

  • The meaning of while (1) is straightforward to deduce by someone who has never seen it, whereas the meaning of for (;;) is not.

There are minor advantages (from the reader's point of view) to for (;;):

  • for (;;) has no expression to read, while while (1) does. (Note the addition of loop { ... } in Perl 6.)

  • "(;;)" can be read as "ever". "For ever" sounds better than "while one", "while true" or "while ever" (and requires no mental backtracking). "While not done" would be a great reading, but translating "1" to "not done" is a stretch.

  • for (;;) is visually distinctive from naturally ending loops.

Update: hum... while (!0) could be read as "while not done"...

Replies are listed 'Best First'.
Re^5: last in a do while loop (for (;;))
by Jenda (Abbot) on Nov 04, 2006 at 00:08 UTC

    Well, we could write while (not 'done') { ... }, but even though it would work and it would read fine, I think it would actually confuse people ;-)

    Update: while ('not done') { ... } of course. Sorry. I guess I should not be here at 1am. Thanks Sidhekin.

Re^5: last in a do while loop (for (;;))
by JimmyDa (Initiate) on Jan 23, 2008 at 16:32 UTC
    Don't know if/when this will get looked at but I was unaware that a do-while loop didn't operate like a loop so last doesn't "work" with it. My problem is I have a structure similar to this. I'm guessing what I need is a way to keep reading the next line in the file, but at times I had problems assigning $aVar = <AFile>. Would a similar loop construct with $aVar = <Afile> being the final statement in that bare loop work?
    while(<AFile>) { if(found keyword) do{ process keyword and next few lines if(done processing){ last } }while(<AFile>); # do some post processing } # Continue processing after this in the same file

      For starters, I'm not sure why this is in this thread. You might benefit from starting a new one since more eyes will see your post.

      Sounds very convoluted. Have you thought about using functions? Not sure what your data looks like, so this may not fit without modification:

      sub read_block { my ($fh) = @_; my $header = <$fh>; return undef if !defined($header); my @block = $header; do { my $line = <$fh>; die "Unexpected end of file\n" if !defined($line); chomp($line); push @block, $line; while ($line !~ /footer/); return \@block; } while (my $block = read_block($fh)) { ...process block... }
        Did it here as I didn't feel like it needed a completely new topic. I'll probably stick with the bare block in the future. The data is generated by a program that does some artificial splitting of the lines if it has over 80 characters in a line so... to do anything useful with the data the lines need to be reordered. Thanks both of u.
      Update: Duplicative, nothing new here, move along.

      Add a block or single-pass loop around your do while.

      my $i = 0; { do { print $i++, $/; last if $i == 2; } while ( $i < 4); }
      Be well,
      rir

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