in reply to Re: Re: for loop localisation bug?
in thread for loop localisation bug?

Ah! But what about 

my $i;
for $i ( 0 .. 10 ) { last if $i == 5; }
print $i;

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This could equally be optimised to remove the loop, but optimising the iterator away would be an error. In this case, the modification of the iterator is the primary purpose of the loop.

Of course, this is grossly simplified, the break condition would not be a comparison against a constant, and in the original scenario, the iterator was being used as the index into an array. In other words, the loop was searching an array for a particular value and the desired outcome is the index of the array at which it is found.

This isn't exactly an unusual use of a for loop

How would this be done in Turing?

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail
Hooray!

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Re: Re: Re: Re: for loop localisation bug?
by demerphq (Chancellor) on Dec 29, 2003 at 19:22 UTC

    Well, depending on the rest of the code, and the sophistication of the compiler one could postulate reasonably that it might be optimised to 

    print 5;

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    As for Turing you would say (and I forget most of my turing so ill write in Perl as if it were Turing) 

    my $value;
for $i (0..10) {
  if ($i==5) {
    $value=$i;
    last;
  }
}
print $value;

    [download]

    Actually thats much the same as what you need to do in Perl anyway (if you are interested in the value of the iterator afterwards.) IMo, its arguable that you would be better served by a while loop anyway, at least thats what I usually do in this type of scenario.

    Oh, Happy New Year mate. :-)


    ---
    demerphq

      First they ignore you, then they laugh at you, then they fight you, then you win.
      -- Gandhi

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