Cacher is the code snippet organizer for pro developers

-- 再帰(chapter4)
tri_number :: Int -> Int
tri_number n
    | n == 0 = 0
    | otherwise = n + tri_number (n-1)

tetration :: Integer -> Integer -> Integer
tetration n m
    | m == 0 = 1 
    | otherwise = (n^) $ tetration n (m-1)

index :: Int -> [a] -> a
index n (x:xs)
    | 0 > n = error "index outbounded"
    | length xs < (n-2) = error "index outbounded"  
    | n == 0 = x
    | otherwise = index (n-1) xs

even_odd :: [Int] -> ([Int], [Int])
even_odd [] = ([], [])
even_odd (x:xs)
    | even x = (fst (even_odd xs), x:snd (even_odd xs))
    | otherwise = (x:fst (even_odd xs), snd (even_odd xs))

-- 挿入ソート
insert :: Ord a => [a] -> a -> [a]
insert [] n = [n]
insert xs n = let xss = span (<n) xs
                in fst xss ++ [n] ++ snd xss

isort :: Ord a => [a] -> [a]
isort [] = []
isort (x:xs) = insert (isort xs) x

-- 分割数
part_num :: Int -> Int
part_num n = part_num' n 1

part_num' :: Int -> Int -> Int
part_num' n m
    | n == m = 1
    | n-m >= m = (part_num' n (m+1)) + part_num' (n-m) m
    | otherwise = part_num' n (m+1)