OverloadedStrings

The most important extension

Posted on 2020-04-03

With this extension classic string literals (of type [Char]) gets wrapped in the fromString from the IsString class in Data.String:

class IsString a where
  fromString :: String -> a

So, for example, this,

{-# LANGUAGE OverloadedStrings #-}
import Data.Text as T

main = T.putStrLn "this is a string"

would get turned into this:

import Data.String
import Data.Text as T

main = T.putStrLn (fromString "this is a string")

Got a type that wants to join the party and be representable by strings? Then make it an instance IsString.

Should probably be always on in Haskell 2020.

Got an issue with any of this? Please share or drop me a line (see below).