problem116.ktn

define unwrap<T> (Optional<T> -> T +Fail):
  -> opt;
  match (opt)
    case none:
      "unwrap error" abort
    case some:
      0 drop // Pass

define f (Int32, Int32 -> Int64 +Fail +IO):
  -> n, c;
  [] -> gray;
  [] -> col;
  gray 1i64 append -> gray;
  col 1i64 append -> col;
  n c gray col 1 f_outer

define f_outer (Int32, Int32, List<Int64>, List<Int64>, Int32 -> Int64 +Fail):
  -> n, c, gray, col, i;
  if (i > n):
    col n get unwrap -> ntmp;
    ntmp - 1i64
  else:
    i - c -> ic;
    match (col ic get)
      case none:
        0i64
      case some:
        0 drop // Pass
    -> g;
    gray g append -> gray;
    gray i 0 f_inner -> r;
    r + g -> rg;
    col rg append -> col;
    i + 1 -> i1;
    n c gray col i1 f_outer

define f_inner (List<Int64>, Int32, Int32 -> Int64 +Fail):
  -> gray, i, j;
  if (j >= i):
    0i64
  else:
    gray i (j + 1) f_inner -> rest;
    gray j get unwrap -> fst;
    fst + rest

50 2 f -> a;
50 3 f -> b;
50 4 f -> c;
(a + b + c) say