Question

我在运行这个Haskell代码时遇到了这个非常烦人的错误。出于某种原因，它不喜欢第一行delLast :: (Ord a) => [a] -> [a]

delLast :: (Ord a) => [a] -> [a]
delLast [] = []
delLast (x:[]) = []
delLast (x:xs) = [x] ++ delLast xs

任何人都知道我为什么会收到这个错误？感谢。

这是我得到的错误：

parse error on input `='
Failed, modules loaded: none.

Answer 1

该行之前是否有未终止的定义？

x = do

delLast :: (Ord a) => [a] -> [a]
delLast [] = []
delLast (x:[]) = []
delLast (x:xs) = [x] ++ delLast xs

编译给我：

test.hs:5:12: parse error on input `='

Answer 2

怎么样？

delLast [] = []
delLast xs = init xs

或者如果你想按自己的方式去做，但更好

delLast :: (Ord a) => [a] -> [a]
delLast [] = []  
delLast [x] = []                  -- Looks better IMO
delLast (x:xs) = x : delLast xs   -- : instead of ++ gives a performance boost

输入`='解析错误 - Haskell

2 个答案: