Comment faire fonctionner l'extension de langue OverloadedStrings?

Question

J'ai activé les chaînes surchargées, mais je ne peux pas les amener à travailler:

$ cat overloadedstrings.hs 
{-# LANGUAGE OverloadedStrings #-} 

import qualified Data.ByteString as B 
import qualified Data.ByteString.Lazy as BL 

lazy :: BL.ByteString 
lazy = "I'm a lazy ByteString" 

strict :: B.ByteString 
strict = "I'm a strict ByteString" 

$ ghci 
GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help 
Loading package ghc-prim ... linking ... done. 
Loading package integer-gmp ... linking ... done. 
Loading package base ... linking ... done. 
Prelude> :l overloadedstrings.hs 
[1 of 1] Compiling Main    (overloadedstrings.hs, interpreted) 

overloadedstrings.hs:7:7: 
    No instance for (Data.String.IsString BL.ByteString) 
     arising from the literal `"I'm a lazy ByteString"' 
        at overloadedstrings.hs:7:7-29 
    Possible fix: 
     add an instance declaration for 
     (Data.String.IsString BL.ByteString) 
    In the expression: "I'm a lazy ByteString" 
    In the definition of `lazy': lazy = "I'm a lazy ByteString" 

overloadedstrings.hs:10:9: 
    No instance for (Data.String.IsString B.ByteString) 
     arising from the literal `"I'm a strict ByteString"' 
        at overloadedstrings.hs:10:9-33 
    Possible fix: 
     add an instance declaration for (Data.String.IsString B.ByteString) 
    In the expression: "I'm a strict ByteString" 
    In the definition of `strict': strict = "I'm a strict ByteString" 
Failed, modules loaded: none. 

Où dois-je importer les instances IsString pour ByteString de? Cela ne devrait-il pas arriver automatiquement? Qu'est-ce que je fais mal?

Answer 1

Vous devez importer les modules .Char8, tels que Data.ByteString.Char8 et Data.ByteString.Lazy.Char8