Let In 语句错误

Question

我对下面的 haskell 语句有疑问：

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“=”时出现解析错误（错误出现在第三行）。

Answer 1

问题是let第二行的缩进：

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 []