Question 1: Prolog systems are not always able to decide whether or not a clause will apply prior to executing it. The precise circumstances are implementation dependent. That is, you cannot rely on that decision in general. Systems do improve here from release to release. Consider as the simplest case: ?- X = 1 ; … Read more
List comprehensions (in fact, Monad comprehensions) can be desugared into do notation. do i <- [1..4] j <- [i+1..4] return (i,j) Which can be desugared as usual: [1..4] >>= \i -> [i+1..4] >>= \j -> return (i,j) It is well known that a >>= \x -> return b is the same as fmap (\x -> … Read more
Implementation which does not stack-overflows: let splitList list = List.foldBack (fun x (l,r) -> x::r, l) list ([],[])
>>> from itertools import count, groupby >>> L=[1, 2, 3, 4, 6, 7, 8, 9, 12, 13, 19, 20, 22, 23, 40, 44] >>> G=(list(x) for _,x in groupby(L, lambda x,c=count(): next(c)-x)) >>> print “,”.join(“-“.join(map(str,(g[0],g[-1])[:len(g)])) for g in G) 1-4,6-9,12-13,19-20,22-23,40,44 The idea here is to pair each element with count(). Then the difference between the … Read more
Play around with this: var elements = [“a”, “b”, “c”, “d”, “e”, “a”, “b”, “c”, “f”, “g”, “h”, “h”, “h”, “e”]; var map = Map(); elements.forEach((element) { if(!map.containsKey(element)) { map[element] = 1; } else { map[element] += 1; } }); print(map); What this does is: loops through list elements if your map does not have … Read more
Both your code and nub have O(N^2) complexity. You can improve the complexity to O(N log N) and avoid using elem by sorting, grouping, and taking only the first element of each group. Conceptually, rmdups :: (Ord a) => [a] -> [a] rmdups = map head . group . sort Suppose you start with the … Read more
Depending on what you want, there are two ways to do this: If you want to do this in “Edit mode”: You must enable “Edit mode” on the list before a selection matters. From the interface for List: /// Creates an instance. /// /// – Parameter selection: A selection manager that identifies the selected row(s). … Read more
I’ll give a bit of an explanation of how it works internally. First, you must realise that Haskell uses a thing called a thunk for its values. A thunk is basically a value that has not yet been computed yet — think of it as a function of 0 arguments. Whenever Haskell wants to, it … Read more