I like that book analogy!

My preference would be to check my context. If a list made sense I would return a list of the number of letters on each page. If it didn't I would add up the number of letters on each page, then add those up. So my previous piece of code becomes this:

sub length {
  if (1 == @_) {
    return CORE::length(shift);
  }
  else {
    my @lengths = map {CORE::length($_)} @_;
    if (wantarray) {
      return @lengths;
    }
    else {
      my $tot = 0;
      $tot += $_ foreach @lengths;
      return $tot;
    }
  }
}
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Note how this falls naturally out of length being the length of a string, and thinking of Perl as being list-oriented...