Hi, the patch below is a trivial change to the merge helper function of Data.List.sort. Its effect is that the first argument of merge is evaluated before the second argument instead of vice versa. I think it's obviously correct. Also, sort is necessarily strict in the whole list, so there can be no loss of laziness. Rationale: The change helps to avoid a stack overflow in the common case where each element of a list depends on the previous one. Examples for such lists are '[1..]' or uses of 'iterate f' where f is a strict function. I believe this case is far more common than the opposite case where each element of the list depends on the next one, so the patch below is an improvement. See also http://thread.gmane.org/gmane.comp.lang.haskell.cafe/30598 Bertram Wed Nov 21 11:14:58 CET 2007 Bertram Felgenhauer * Data.List.sort: force elements from start to end. this prevents a stack overflow on sort (take 10^6 [1..])