[GHC] #12049: `OverloadedStrings` for types

12 May 2016

      #12049: `OverloadedStrings` for types
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           Reporter:  Iceland_jack   |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
           Keywords:                 |  Operating System:  Unknown/Multiple
  CustomTypeErrors                   |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Is there any sense in adding

 {{{#!hs
 class IsSymbol a where
   type FromSymbol (str :: Symbol) :: a

 instance IsSymbol ErrorMessage where
   type FromSymbol str = GHC.TypeLits.Text str

 instance IsSymbol ErrorMessage where
   type FromSymbol str = str
 }}}

 where `FromSymbol` gets placed before type-level string literals:

 {{{#!hs
 TypeError ("Warning: ":<>:ShowType ty:<>:" is odd.")
 }}}

 analogous to `Data.String.IsString`.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12049
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