Haskellのマージソートの実装では、コンパイルが、ここでは何も

Question

を返さない私の実装です：私はそれ私のマシンがクラッシュを実行したときに

mergesort :: (Ord a) => [a] -> [a] 
mergesort list = merge (mergesort (left list)) (mergesort (right list)) 
    where 
    left xs = take (div (length xs) 2) xs 
    right xs = drop (div (length xs) 2) xs 
    merge [] ys = ys 
    merge xs [] = xs 
    merge (x:xs) (y:ys) 
     | x <= y = x : merge xs (y:ys) 
     | otherwise = y : merge (x:xs) ys 

コードがコンパイルされますが。私は間違って何をしていますか？

Answer 1

基本ケースがないため、無限の再帰が発生します。 []または[1]のようなリストを使ってあなたの例を進めてみると、問題に直面するでしょう。

mergesort :: (Ord a) => [a] -> [a] 
mergesort [] = [] -- < ADDED 
mergesort [x] = [x] -- < ADDED 
mergesort list = merge (mergesort (left list)) (mergesort (right list)) 
    where 
    left xs = take (div (length xs) 2) xs 
    right xs = drop (div (length xs) 2) xs 
    merge [] ys = ys 
    merge xs [] = xs 
    merge (x:xs) (y:ys) 
     | x <= y = x : merge xs (y:ys) 
     | otherwise = y : merge (x:xs) ys