haskell - 输入“=”时解析错误 - Haskell

Question

当我运行这个 Haskell 代码时，我遇到了这个非常烦人的错误。由于某种原因，它不喜欢拳头线delLast :: (Ord a) => [a] -> [a]

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

有谁知道我为什么会收到这个错误？谢谢。

这是我得到的错误：

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

Answer 1

在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

编译给了我：

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

Answer 2

关于什么

delLast [] = []
delLast xs = init xs

或者如果你想按照自己的方式做，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