If you do not know what a closure is, the following explanation probably won't help much.

1. With the C-style for loop, the subroutine sub{ print "Test $i \n"; } is closing over the variable $i.

   That is, the value of the variable within the string is not interpolated until the subroutine is run, and by the time it is run, $i retains the last value it had when the loop completed -- Ie. 10 -- for all instances of the subroutine.

2. With the foreach-style for loop; the subroutines are closing over aliases to the values produced by the range operator in the for loop.

   Thus each instance of the subroutine is closing over an alias to a different constant value, 1 .. 10.