Re: Easiest way to do something only on first iteration of loop

Several good ways to do this have already been mentioned for Perl 5.

I'll also note that your question was one of the many things addressed in Perl6.

Perl 6 added an explicit phaser for first loop invocation you can use like this:

   for @arr -> $line {
      FIRST { print ' ' xx $indentation };
      say $line;
   }
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Re^2: Easiest way to do something only on first iteration of loop by ibm1620 (Hermit) on May 09, 2016 at 14:43 UTC
I only realized now that all of the above solutions have the condition backward: the first time through the loop I don't want to print an indentation. An outer routine has already typed a "header", like a number or a bullet, to the left and the print-head is now positioned at the indentation column at the time the subroutine is called. The first line must be printed without further indentation, but any subsequent lines will need indentation. Interestingly, it was only when reading the Perl 6 syntax that this leaped out at me. For my purpose I'd need the NEXT phaser rather than the FIRST phaser. Thanks for the tip.	[reply]
Re^3: Easiest way to do something only on first iteration of loop by Anonymous Monk on May 09, 2016 at 17:41 UTC
Then you haven't looked at Re: Easiest way to do something only on first iteration of loop. Also I wonder how many of those above solutions have actually been tested, since most of them still have `sub display_paragraph() {` [download] mandating zero arguments for a sub that is called with two arguments.	[reply] [d/l]