Question

我正在尝试将一个整数读取为Text：

-- This works
mm x = do 
        T.putStrLn "Testing x being input as Text"
        T.putStrLn x
        -- y <- x * 2
        -- putStrLn y

mm "10"

生产

Testing x being input as Text
10

太好了。如果以Text开头，则可以使用。很好。

但是

-- This does not work
mm2 x = do 
        T.putStrLn "Testing x being input as an integer and converted to Text"
        let m = tshow x
        T.putStrLn m
        -- y <- x * 2
        -- putStrLn y

mm2 10

<interactive>:3:17: error:
    • Variable not in scope: tshow :: p -> t
    • Perhaps you meant ‘show’ (imported from Prelude)

从here我了解到tshow：

tshow :: Show a => a -> Text

应该存在于Prelude中，并且应该将其转换为文本。

常规（非常规）show也会失败：

-- This does not work
mm2 x = do 
        T.putStrLn "Testing x being input as an integer and converted to Text"
        let m = show x
        T.putStrLn m
        -- y <- x * 2
        -- putStrLn y

mm2 10

使用

<interactive>:4:20: error:
    • Couldn't match type ‘String’ with ‘Text’
      Expected type: Text
        Actual type: String
    • In the first argument of ‘Data.Text.IO.putStrLn’, namely ‘m’
      In a stmt of a 'do' block: Data.Text.IO.putStrLn m
      In the expression:
        do Data.Text.IO.putStrLn "Testing x being input as an integer and converted to Text"
           let m = show x
           Data.Text.IO.putStrLn m

也是

-- This does not work
mm2 x = do 
        T.putStrLn "Testing x being input as an integer and converted to Text"
        let m = T.pack x
        T.putStrLn m
        -- y <- x * 2
        -- putStrLn y

mm2 10

使用

<interactive>:1:5: error:
    • No instance for (Num String) arising from the literal ‘10’
    • In the first argument of ‘mm2’, namely ‘10’
      In the expression: mm2 10
      In an equation for ‘it’: it = mm2 10

我如何阅读/显示/打包/投射一个整数作为文本？很难做到我在做什么错了？

更新1

还有

-- This does not work
import qualified Data.Text.IO as T
import qualified Data.Text as TS
mm2 x = do 
        T.putStrLn "Testing x being input as an integer and converted to Text"
        let m = T.tshow x
        T.putStrLn m
        -- y <- x * 2
        -- putStrLn y

mm2 10

生产

<interactive>:3:17: error:
    Not in scope: ‘T.tshow’
    No module named ‘T’ is imported.

更新2

还有

mm2 x = do 
        T.putStrLn "Testing x being input as an integer and converted to Text"
        let m = TS.tshow x
        T.putStrLn m
        -- y <- x * 2
        -- putStrLn y

mm2 10

产生

<interactive>:3:17: error:
    Not in scope: ‘TS.tshow’
    No module named ‘TS’ is imported.

Answer 1

我仍然不清楚tshow的位置以及为什么它出现在Hoogle上，但是无法从Prelude，Data.Text或Data.Text.IO导入。

但这会正确执行：

mm2 x = do 
        T.putStrLn "Testing x being input as an integer and converted to Text"
        let m = T.pack $ show x
        T.putStrLn m
        -- y <- x * 2
        -- putStrLn y

mm2 10

首先从show到Prelude，然后从Integer -> String到T.pack。

在Haskell中读取数字作为Text，tshow和show

更新1

更新2

1 个答案: