Judah Jacobson wrote:
This means that the library version produces a stack overflow on lists generated in an iterate like fashion (say, take 1000000 [0..]). The modified version produces a stack overflow on the reverse of that list, but I believe such lists are much rarer in practice.
Bertram, are you sure that's right?
Yes.
There's already a stack overflow in "take 1000000 [0..]" itself (try just "last $ take 1000000 [0..]"). See the bug http://hackage.haskell.org/trac/ghc/ticket/1997
No, that's not quite right. The stack overflow happens on evaluating the last element of that list *without evaluating the previous elements first*. To wit, Prelude Data.List> foldl' (+) 0 $ take 1000000 [0..] 499999500000 Prelude Data.List> last $ take 1000000 [0..] *** Exception: stack overflow or Prelude> let t = take 1000000 [0..] Prelude> last t *** Exception: stack overflow Prelude> t !! 500000 500000 Prelude> last t 999999 Bertram