haskell - 为什么GHCi没有显示与GHC相同的错误消息

Question

关于Haskell type error on compilation中给出的错误的推理，我发现GHCi的行为异常
test.hs

members :: String -> Bool;
members str = and [ b | x <- str, b <- map (elem x) "abcde" ]

产生以下错误信息

Prelude> :l test.hs
[1 of 1] Compiling Main             ( test.hs, interpreted )

test.hs:2:53: error:
    • Couldn't match type ‘Char’ with ‘t0 Char’
      Expected type: [t0 Char]
        Actual type: [Char]
    • In the second argument of ‘map’, namely ‘"abcde"’
      In the expression: map (elem x) "abcde"
      In a stmt of a list comprehension: b <- map (elem x) "abcde"

而
GHCi

Prelude> members :: String -> Bool; members xs = and [ b | x <- xs, b <- map (elem x) "abcde"]

产生

<interactive>:18:78: error:
    • Couldn't match type ‘Char’ with ‘[Char]’
      Expected type: [[Char]]
        Actual type: [Char]
    • In the second argument of ‘map’, namely ‘"abcde"’
      In the expression: map (elem x) "abcde"
      In a stmt of a list comprehension: b <- map (elem x) "abcde"

更新资料

我还不明白的是，为什么GHC省略了 Foldable t0类约束-我
本来希望错误消息是这样的:

test.hs:2:53: error:
    • Couldn't match type ‘Char’ with ‘t0 Char’
      Expected type: Foldable t0 => [t0 Char]
        Actual type: [Char]
    • In the second argument of ‘map’, namely ‘"abcde"’
      In the expression: map (elem x) "abcde"
      In a stmt of a list comprehension: b <- map (elem x) "abcde"

Answer 1

由FTP(Foldable-Traversable-Proposal)函数引入的elem具有
获得了新的类型签名。

elem :: (Eq a, Foldable t) => a -> t a -> Bool

而且似乎GHCi使用了 ExtendedDefaultRules扩展名，可以通过以下方式停用该扩展名:

:set -NoExtendedDefaultRules

这个扩展名和 trac:10971使得 Foldable和 Traversable默认为 []。

更新

没有显示类约束，因为对它的类型检查是在以后的阶段完成的。