#!/usr/bin/perl -w

use v5.10.1;

my @array = qw/one two three/;

while (my ( $index, $line ) = each @array) {
  print "$index: $line\n";
}

Result:
Type of arg 1 to each must be hash (not private array) at ./t8 line 7, near "@array) "
Execution of ./t8 aborted due to compilation errors.