The key to understanding difference lists is understanding what they are on the level of the nested compound term that represents lists. Normally, we see a list like that: [a, b, c] This is now a list with three elements. The exactly same nested term using the dot as the list functor, ./2, and the … Read more
You mean something like this? quicksort [] = [] quicksort (x:xs) = quicksort less ++ (x : equal) ++ quicksort more where (less, equal, more) = partition3 x xs partition3 _ [] = ([], [], []) partition3 x (y:ys) = case compare y x of LT -> (y:less, equal, more) EQ -> (less, y:equal, more) … Read more
The definition of flatten2/2 you’ve given is busted; it actually behaves like this: ?- flatten2([a, [b,c], [[d],[],[e]]], R). R = [a, b, c] ; false. So, given the case where you’ve already bound R to [a,b,c,d,e], the failure isn’t surprising. Your definition is throwing away the tail of lists (ListTail) in the 3rd clause – … Read more
The problem in ((((a ++ b) ++ c) ++ d) ++ e) ++ f is the nesting. The applications of (++) are left-nested, and that’s bad; right-nesting a ++ (b ++ (c ++ (d ++ (e ++f)))) would not be a problem. That is because (++) is defined as [] ++ ys = ys (x:xs) … Read more