Wow, I have a split personality today.

I agree that error handling is the real bugbear of single-return. Special additional logic and/or an extra state variable are often required to make it work. It makes code less clear and sometimes even more error-prone. "Break out now" makes the most logical sense in a failure case.

But I see this example as different: there is one kind of result that could be created in one of two different ways. The if statement doesn't add any complexity to the code--you have to check for definedness somehow. Nor does it hurt clarity. Why is indenting so bad?

This is not to say that I object to your preferred solution. I think that's fine, too.

There's nothing really wrong with indenting apart from making your code narrower. (This split personality adheres to the 80-character-per-line rule.) Excessive indentation, however, is a code smell to me. I usually accept about four levels: one for the function, two for a nested loop, and the last one for a potential if block inside the loop. Anything more and I try to break it into smaller functions. (And I just habitually minimise indentation as I feel it makes it easier to follow the overall logic.)

There's an easy solution to that: ;-)

package Foo {
  sub foo {
    ...;
    while (my $row = $st->fetchrow_array) {
      ...;
      for my $value (split /,/ $row->[3]) {
        if ($value == 0) {

...;
while (not $finished) {
  ...;
  if ($happy) {
    $finished++;
    if (@complaints) {
      while (defined(my $c = shift @complaints)) {
        ...;
      }
    }
  }
}
...;

        }
      }
    }
    ...;
  }
}
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perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'