Please don't produce this kind of code except in fun.

But since you ask, the trick is recursion. Here it is broken out:

sub r {
  my $s;
  $s .= chop for @_ = @_;
  $s . 0 ?
    ( &r , $s ) :
    ()
}
[download]

and now with better variable names, fewer implicit variables, rewritten loops, that kind of thing:

sub recursive_s2a {
  my $str_last;
  foreach my $str (@_ = @_) {
    $str_last .= chop($str);
  }

  if ($str_last . 0) {
    return (recursive_s2a(@_) , $str_last );
  }
  else {
    return;
  }
}
[download]

And now you see that the function creates the last string in the list to produce, tests whether that was the empty string, if it was it returns nothing, if it wasn't it then proceeds by recursion to generate the first strings, and adds the string it produced to that list.

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