重現我試圖檢查this stackoverflow answer與ghci的，並得到了以下錯誤： > import Data.List
> let m = head . sort
> m [2,3,4]
<interactive>:5:4:
No instance for (Num()) arising from the literal `2'
Possible fix
考慮以下人爲的例子內的值： module Main where
myadd3 first second third =
let result1 = first -- line 3
result2 = second -- line 4
result3 = third -- line 5
in result1 + result2 + re
我試圖理解爲什麼類型： (flip .) is: (a -> a1 -> b -> c) -> a -> b -> a1 -> c 首先，類型： flip: is (a -> b -> c) -> b -> a -> c (.): is (b -> c) -> (a -> b) -> a -> c 我將重命名變量更清晰在我的解釋中，所以類型： flip: is (ax -> bx -> cx) -
說我有一個整數l = [1,2] ，我想打印到stdout的名單。 做print l產生[1,2] 說我想要打印的清單沒有括號 map print l產生 No instance for (Show (IO())) arising from a use of `print'
Possible fix: add an instance declaration for (Show (IO()))
我正在學習haskell，我正在嘗試編寫一些簡單的函數。一切運作良好，直到我使用功能isUpper。我無法編譯，因爲這個錯誤的項目： [1 of 1] Compiling Main (C:\Users\...\src\Main.hs, interpreted)
C:\Users\...\src\Main.hs:147:25:
Not in scope: `isUpper'
Fa