use warnings; 
use strict;  
 
my $ref = ['a',['b','c'],'d',['e','f']]; 
for my $x (@{$ref}) { 
   if (ref($x) eq 'ARRAY') { 
      for my $y (@{$x}) { 
         print "-$y\n"; 
      } 
   } 
   else { 
      print "$x\n"; 
   } 
}

use warnings;  
use strict;   
  
my $ref = ['a',['b','c'],'d',['e',['y','z'],'f']];  
my $depth = 0;  
process($ref);   
  
sub process {  
   my $aref = shift;  
   for my $x (@{$aref}) {  
      if (ref($x) eq 'ARRAY') {  
         $depth++;  
         process($x);  
         $depth--;  
      }  
      else {  
         print "$depth $x\n";  
      }  
   }  
}   
  
__END__  
Prints out:  
0 a  
1 b  
1 c  
0 d  
1 e  
2 y  
2 z  
1 f