Haskell Merge Sort

Question

Dies ist eine Implementierung von Mergesort mit Funktionen höherer Ordnung, Wachen, wo und Rekursion.

jedoch einen Fehler von Compiler bekommen 6:26: parse error on input ‘=’

mergeSort :: ([a] -> [a] -> [a]) -> [a] -> [a] 
    mergeSort merge xs 
     | length xs < 2 = xs 
     | otherwise = merge (mergeSort merge first) (mergeSort merge second) 
     where first = take half xs 
       second = drop half xs 
       half = (length xs) `div` 2 

ich nicht, was falsch sehen kann? oder ich verstehe den Compiler nicht.

Answer 1

Haskell ist eine indentation-sensitive Programmiersprache, die Sie einfach reparieren müssen (wenn Sie Tabulatoren verwenden, ändern Sie das zur Verwendung von Leerzeichen).

mergeSort :: ([a] -> [a] -> [a]) -> [a] -> [a] 
mergeSort merge xs 
     | length xs < 2 = xs 
     | otherwise = merge (mergeSort merge first) (mergeSort merge second) 
     where first = take half xs 
       second = drop half xs 
       half = length xs `div` 2 

Answer 2

Weitere msort Implementierung in Haskell;

merge :: Ord a => [a] -> [a] -> [a] 
merge [] ys   = ys 
merge xs []   = xs 
merge (x:xs) (y:ys) | x < y  = x:merge xs (y:ys) 
        | otherwise = y:merge (x:xs) ys 

halve :: [a] -> ([a],[a]) 
halve xs = (take lhx xs, drop lhx xs) 
      where lhx = length xs `div` 2 

msort :: Ord a => [a] -> [a] 
msort [x] = [x] 
msort xs = merge (msort left) (msort right) 
      where (left,right) = halve xs