in reply to Useful uses of redo?

Apparently, if your used to using do/while loops in p5, your gonna have to replace them with some hooky construction of

  1. A bare block.
  2. A last if condition
  3. And a redo

in P6!?

Which seems like a completely retrograde step to me. Apparently this is because "people often use do/while wrongly...". By my reckoning, if we applied that logic to the rest of perl, we'd be left with scalar assignment and if/goto. Hey! Fortran IV.

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail
"Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon

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Re^2: Useful uses of redo?
by ikegami (Patriarch) on Aug 26, 2004 at 19:12 UTC

    I guess you can do:

    {                       # do {
   stmt;
   stmt;
   stmt;
   redo if $cond;       # } while ($cond);
}

    [download]

    and

    {                       # repeat {
   stmt;
   stmt;
   stmt;
   redo unless $cond;   # } until ($cond);
}

    [download]

    but why? yuck! It's like saying that while loops while henceforth be like:

    {
   last unless $cond;    # while ($cond)
   stmt;
   stmt;
   stmt;
   redo;                 # wend
}

    [download]
[reply]
[d/l]
[select]
      do { } still exists. It's just the statement-modifier while-on-do that is taken away.
[reply]
[d/l]
        So are you saying that in perl6 the following won't be valid: 
        do {
    $foo = foo();
    $bar = bar();
} while ($foo != $bar);
        ?? That would suck!
[reply]
Re^2: Useful uses of redo?
by lidden (Curate) on Aug 27, 2004 at 08:35 UTC
    In Perl 6 that is done by 
    loop {
    # do something
    last if $done;
}

    [download]
[reply]
[d/l]

      Okay, we've traded a simple, extensible, easily used and self-documenting construct for YAKW and less self documenting code.

      I often use 

      ...
my( $p, $i ) = 0;
$p += $i while $i = 1+index $haystack, $needle, $i;
...

      [download]

      Sometimes, when debugging I need to see what is going on, so I wrap the code and add some debug: 

      ...
my( $p, $i ) = 0;
do{ 
    $p += $i;
    print "$p : $i, other stuff";
} while $i = 1+index $haystack, $needle, $i;
...

      [download]

      Once I'm done debugging, I can just comment out the print lines and I am back to where I was.

      In p6, I will have to completely change the coding of the single line with modifier version of the loop to an alien and less clear construct when I need to debug, and convert it back once I have the logic correct. Or leave as that strangly Fortran IV-ish form: 

      my( $p, $i ) = 0;
loop {
    $p += $i;
    last if $i = 1+index $haystack, $needle, $p;
}

      [download]

      I know "LW is always right" and "LW is always right even when he is wrong", but on this I think he has never been more right.

      Examine what is said, not who speaks.
      "Efficiency is intelligent laziness." -David Dunham
      "Think for yourself!" - Abigail
      "Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon
[reply]
[d/l]
[select]
        From the limited evidence of this particular article, you seem to be unaware that you've switched from test-before semantics to test-after semantics, which can completely foul things up on loops that need to be able to execute 0 times, or that have side effects in the conditional. So it's quite possible you've just proven the argument you were trying to disprove. :-)
[reply]
[d/l]

In Section Seekers of Perl Wisdom