[GHC] #9842: No Typeable instance for type-level literals

27 Nov 2014

      #9842: No Typeable instance for type-level literals
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       Reporter:  Feuerbach          |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.8.3
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 There's no Typeable instance for string and numeric literals. E.g.

 {{{
 Prelude GHC.TypeLits Data.Typeable> typeRep (Proxy :: Proxy "foo")

 <interactive>:15:1:
     No instance for (Typeable "foo") arising from a use of ‘typeRep’
     In the expression: typeRep (Proxy :: Proxy "foo")
     In an equation for ‘it’: it = typeRep (Proxy :: Proxy "foo")
 }}}

 This means that we can't have a Typeable instance for phantom types
 parameterised by these literals.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9842
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