Haskell 使用 OverloadedStrings，但仍然出现 [Char] 错误

Question

我从 and 这样的问题中了解到，使用 PRAGMA OverloadedStrings 意味着我应该能够使用文本作为我的字符串类型。

但是，当我用文本测试 my data types 时，出现以下错误：

$ stack ghci
Prelude> :l myfile.hs
Ok, one module loaded.
*Main> Rec "asd" "m"

<interactive>:46:5: error:
    • Couldn't match expected type ‘Text’ with actual type ‘[Char]’
    • In the first argument of ‘Rec’, namely ‘"asd"’
      In the expression: Rec "asd" "m"
      In an equation for ‘it’: it = Rec "asd" "m"

<interactive>:46:11: error:
    • Couldn't match expected type ‘Text’ with actual type ‘[Char]’
    • In the second argument of ‘Rec’, namely ‘"m"’
      In the expression: Rec "asd" "m"
      In an equation for ‘it’: it = Rec "asd" "m"

我的代码如下：

{-# LANGUAGE DeriveGeneric,  OverloadedStrings,  DefaultSignatures,  TypeOperators,  FlexibleContexts, RecordWildCards, FlexibleInstances, ExtendedDefaultRules #-}

import qualified Data.Map as Map
import qualified Data.Set as Set
-- import qualified Data.Text as T
import Data.Text (Text)
import GHC.Generics

data Rec  = Rec {
     recCategory :: Text,
     recId :: Text
     } deriving Generic

我做错了什么？

我在 this question 中看到一个建议：

EDIT You may also want to add default (Text) to the top of your module to have it use Text instead of String by default.

但我不清楚允许此默认值的语法是什么

Answer 1

你在你的文件中启用了“OverloadedStrings”，但在 ghci 中并没有启用它。为此，你需要 ˋ:set -XOverloadedStringsˋ。请注意，扩展会影响您编写字符串文字的地方，无论您是否在定义数据类型的地方启用它都没有关系。

Haskell 使用 OverloadedStrings，但仍然出现 [Char] 错误

Haskell using OverloadedStrings, but getting [Char] error anyway

generics

haskell

overloaded-strings