nickel/stdlib/lists.ncl

{
  lists = {
    concat : List -> List -> List = fun l1 l2 => l1 @ l2;

    foldl : forall a. (a -> Dyn -> a) -> a -> List -> a =
      fun f fst l =>
        if length l == 0 then
          fst
        else
          let rest = foldl f fst (tail l) in
          seq rest (f rest (head l));

    fold : forall a. (Dyn -> a -> a) -> List -> a -> a =
      fun f l fst =>
        if length l == 0 then
          fst
        else
          f (head l) (fold f (tail l) fst);

    cons : Dyn -> List -> List = fun x l => [x] @ l;

    filter : (Dyn -> Bool) -> List -> List =
      fun pred l =>
        fold (fun x acc => if pred x then acc @ [x] else acc) l [];

    flatten : List -> List =
      fun l =>
        fold (fun l acc => acc @ Assume(List, l)) l [];

    all : (Dyn -> Bool) -> List -> Bool =
      fun pred l =>
        fold (fun x acc => if pred x then acc else false) l true;

    any : (Dyn -> Bool) -> List -> Bool =
      fun pred l =>
        fold (fun x acc => if pred x then true else acc) l false;
  }
}