无法将预期类型'[a]'与实际类型'a'匹配

Question

为什么这会给我错误？

insertAt :: Int -> a -> [a] -> [a]
insertAt n x xs = x1 ++ x ++ x2
    where (x1,x2) = splitAt n xs

Answer 1

您正在混合列表和列表元素 - 您必须将元素打包在单例列表中

insertAt :: Int -> a -> [a] -> [a]
insertAt n x xs = x1 ++ [x] ++ x2
    where (x1,x2) = splitAt n xs