Haskell中的奇怪編譯錯誤

Question

爲什麼max prod nextProd的類型在下面的函數中被推斷爲Int->Int->Int而不僅僅是Int？

import qualified Data.Vector as DV 

largestProduct::DV.Vector Int->(Int, Int) 
largestProduct digits = foldl lastProdAndMax (0,0) [1..((DV.length digits) - 13)] where 
    lastProdAndMax _ 1 = (first, first) where first = DV.foldl (*) 1 $ DV.take 13 digits 
    lastProdAndMax (prod, max) i = (nextProd, max prod nextProd) 
     where nextProd = (prod `div` ((DV.!) digits (i-13))) * ((DV.!) digits i) 

Answer 1

你的錯誤是在

lastProdAndMax (prod, max) i = (nextProd, max prod nextProd) 
         ^^^ 

在該範圍

，max是Int（超載max功能）。