让语句错误

Question

我遇到以下haskell语句的问题：

insertSort3 xs =
    let sort3 [] ys = ys
         sort3 (x:xs) ys = sort3 xs (insert x ys)
    in sort3 xs []

我的编译器说：输入'='时解析错误（错误发生在第三行）。

Answer 1

问题是let第二行中的缩进：

insertSort3 xs = 
 let sort3 [] ys = ys
     -- the next line should line up with the previous sort3
     sort3 (x:xs) ys = sort3 xs (insert x ys)
 in sort3 xs []