The thing is, I think for (@array) is optimized to take a reference to the array rather putting it in list context (similarly to how for (x..y) is optimized not to flatten the list).

sub f4 {
   for (@_) {
      print($_);
      shift;
   }
   print("\n");
}

sub f5 {
   for ((), @_) {
      print($_);
      shift;
   }
   print("\n");
}

f4(map/./g, Japh);  # Jp
f5(map/./g, Japh);  # Japh
[download]

(Copied from Re^3: For vs. While)

I believe there are 5 kinds of for loops.

• for (x; y; z) (C-style syntax)
• for (x..y) (Not flattened)
• for (ARRAY) (Not flattened)
• for (reverse LIST) (Flattened, but no explicit call to reverse)
• for (LIST)