Steven D'Aprano wrote:
Calling all functional programming fans... is Python's built-in reduce() a left-fold or a right-fold? ... So which is correct? Or is it that different people have different definitions of foldl() and foldr()?
Just test. Floating point addition is not associative, so: >>> a = reduce(float.__add__, (4095 * 2. **n for n in range(100))) >>> b = reduce(float.__add__,(4095*2.**n for n in reversed(range(100)))) >>> a - b 5.7646075230342349e+17 So, since a > b, it must be foldl (the first addition happens to the first of the list). Foldl is the eager-beaver's dream; foldr is the procrastinator's dream. --Scott David Daniels scott.dani...@acm.org -- http://mail.python.org/mailman/listinfo/python-list
