refactor.hs

{-
 public void take(int v) {
    if (currentMode == Mode.accumulating) {
      int digits = (int)Math.pow(10, (int)Math.log10(v) + 1);
      int x = stack.pop();
      x *= digits;
      x += v;
      stack.push(x);
    }

    if (currentMode == Mode.replacing) {
      stack.pop();
      stack.push(v);
      currentMode = Mode.accumulating;
    }

    if (currentMode == Mode.inserting) {
      int top = stack.peek();
      stack.push(top);
      stack.push(v);
      currentMode = Mode.accumulating;
    }
  }
-}

data CurrentMode = Accumulating
                 | Replacing
                 | Inserting
                   deriving Show

takeR :: Int -> (CurrentMode, [Int]) -> (CurrentMode, [Int])
takeR v (Inserting , [])        = (Accumulating, [v])
takeR v (mode      , [])        = error $ "Empty stack not supported for mode: " ++ (show mode)
takeR v (mode      , (x:stack)) = (Accumulating, newStack mode)
    where
      newStack Accumulating = (x * digits + v):stack
      newStack Replacing    = x:stack
      newStack Inserting    = v:x:stack
      digits = 10 ^ (1 + (log10 $ realToFrac v))
      log10 y = floor $ logBase 10 y