for (@array) loops until the number of iterations is greater than the number of elements in the array. When you reached the 3rd iteration of your for loop, @_ only has two elements (because of shift and pop), so the loop exits. 

sub f1 {
   while (@_) {
      print(shift);
   }
   print("\n");
}

sub f2 {
   for (@_) {
      print(shift);
   }
   print("\n");
}

sub f3 {
   for (map $_, @_) {
      print(shift);
   }
   print("\n");
}

f1(map/./g, Japh);  # Japh
f2(map/./g, Japh);  # Ja
f3(map/./g, Japh);  # Japh

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f2 iterates over the elements of @_.
f3 iterates over a premade list on the stack, so it doesn't matter that @_ changes.

In reply to Re: For vs. While by ikegami
in thread For vs. While by Andrew_Levenson

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