Re: For vs. While

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
[download]

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

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Re^2: For vs. While by Andrew_Levenson (Hermit) on Dec 06, 2006 at 00:54 UTC
Ahh, that makes perfect sense. Thanks! `V(qw/74 401 211 79/);sub V{while(@_){$v**=$V?$#_:$V; print(map{$V<$v?chr(shift):chr(reverse(pop))}$_),$V+=$#_%2!=1?1:0}}` [download]	[reply] [d/l]
Re^3: For vs. While by ikegami (Patriarch) on Dec 06, 2006 at 01:10 UTC
That behaviour is specifically for `for (@array)`. `for (@array)` is different than other forms of `for (LIST)`. As soon as one iterates over anything but just an array, it's the size of the list on the stack that matters. The real difference is that `for (@array)` is optimized to avoid flattening `@array` onto the stack. Instead, `for (@array)` navigates `@array` in place. For all other expressions, a list is formed on the stack and `for` iterates over that. The following show the difference between iterating in place, and iterating over a list on the stack. `sub f4 { for (@_) { print($_); shift; } print("\n"); } sub f5 { for ((), @_) { print($_); shift; } print("\n"); } f4(map/./g, Japh); # Jp f5(map/./g, Japh); # Japh` [download]	[reply] [d/l] [select]