Typeclass constraint should pick the OverloadedString type.

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

class    NoDefault a      where noDefault :: a -> Text
instance NoDefault T.Text where noDefault = id

main = print (noDefault "Hello!")

default.hs:7:15:
    Ambiguous type variable `a0' in the constraints:
      (NoDefault a0) arising from a use of `noDefault'
                     at default.hs:7:15-23
      (Data.String.IsString a0) arising from the literal `"Hello!"'
                                at default.hs:7:25-32
    Probable fix: add a type signature that fixes these type variable(s)
    In the first argument of `print', namely `(noDefault "Hello!")'
    In the expression: print (noDefault "Hello!")
    In an equation for `main': main = print (noDefault "Hello!")

Trac metadata

Trac field	Value
Version	7.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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