in reply to Re: {} vs do{}
in thread {} vs do{}

I see. In all the time I've been using Perl, I've sometimes run into times when I tried to use a block in an expression and it doesn't work. Putting do in front makes it work.

Thanks for all the replies, everyone, this holiday.

—John

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Re: Re: Re: {} vs do{}
by MeowChow (Vicar) on Jul 04, 2001 at 23:01 UTC
    Just keep in mind the important caveat that: 
      do { BLOCK } while ( COND );

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    is NOT equivalent to: 
      while ( COND ) { BLOCK }

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    In the first case, the code in BLOCK is executed once before checking the condition. This goes for until as well. However: 
      do { BLOCK } for ( LIST );

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    is equivalent to: 
      for ( LIST ) { BLOCK }

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       MeowChow                                   
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      The condition at the end running once before the test is something I've long known, since the Pascal days. That for doesn't is not something I've thought about.

      $value= "global";

do { print "Inside block: $value\n" }
   for (my $value= 5;  $value < 7;  ++$value);

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      does not compile, so whether the loop variable is set first or later or what the scope is is moot. For the list form, 
      $_= 1;

do { print "Inside block: $_\n" }
   for (5..7);

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      It is intuative that it work the same way, one iteration per item in the list, and you can't use a variable, e.g. 
      do { print "Inside block: $value\n" }
   for my $value (5..7);

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      doesn't compile either. So variable scope issues are avoided.

      Interesting.

      —John

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