小编ton*_*ika的帖子

我正在研究Data.List模块中的代码,并不能完全围绕这种排列实现:

permutations            :: [a] -> [[a]]
permutations xs0        =  xs0 : perms xs0 []
  where
    perms []     _  = []
    perms (t:ts) is = foldr interleave (perms ts (t:is)) (permutations is)
      where interleave    xs     r = let (_,zs) = interleave' id xs r in zs
            interleave' _ []     r = (ts, r)
            interleave' f (y:ys) r = let (us,zs) = interleave' (f . (y:)) ys r
                                     in  (y:us, f (t:y:us) : zs)

有人可以详细解释这些嵌套函数如何相互连接/相互作用？

我将ojdbc6.jar复制到了tomcat安装文件夹中的lib文件夹中。当我部署在JDBC连接中使用Oracle驱动程序的Web应用程序时，服务器会说找不到驱动程序类，并且我被迫手动执行DriverManager.registerDriver，然后它可以工作。

可以这样做，以便在启动时注册驱动程序，而不必创建连接池也不必手动进行？

我在Haskell中实现了两个版本的Merge Sort,如下所示:

mergeSort1 :: (Ord a) => [a] -> [a]
mergeSort1 xs = foldl' (\acc x -> merge [x] acc) [] xs

和

mergeSort2 :: (Ord a) => [a] -> [a]
mergeSort2 [] = []
mergeSort2 (x:[]) = [x]
mergeSort2 xs = (mergeSort2 $ fst halves) `merge` (mergeSort2 $ snd halves)
         where halves = splitList xs

其中'merge'和'splitList'实现如下:

merge :: (Ord a) => [a] -> [a] -> [a]
merge [] [] = []
merge xs [] = xs
merge [] ys …