[GHC] #11051: GHCi with +t option set shows type representations

[GHC]

#11051: GHCi with +t option set shows type representations
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        Reporter:  bgamari           |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 As it turns out generic deriving is also bitten by this,
 {{{
 GHCi, version 7.10.2: http://www.haskell.org/ghc/  :? for help
 λ> :set +t
 λ> :set -XDeriveGeneric
 λ> import GHC.Generics
 λ> data Hello = Hello Int deriving (Eq, Generic)
 abstract C1_0Hello
 abstract D1Hello
 data Hello = Hello Int
 abstract S1_0_0Hello
 }}}

 For the record, `hscDeclsWithLocation` in `HscMain` is responsible for the
 evaluation and generation of `TyThings`. Currently it drops `TyThings`
 corresponding to implicit `TyCons`/`Ids` and `DFunIds`,
 {{{#!hs
     let tcs = filterOut isImplicitTyCon (mg_tcs simpl_mg)
         patsyns = mg_patsyns simpl_mg

         ext_ids = [ id | id <- bindersOfBinds core_binds
                        , isExternalName (idName id)
                        , not (isDFunId id || isImplicitId id) ]
             -- We only need to keep around the external bindings
             -- (as decided by TidyPgm), since those are the only ones
             -- that might later be looked up by name.  But we can exclude
             --    - DFunIds, which are in 'cls_insts' (see Note
 [ic_tythings] in HscTypes
             --    - Implicit Ids, which are implicit in tcs
             -- c.f. TcRnDriver.runTcInteractive, which reconstructs the
 TypeEnv
 }}}

 This would be one place to drop the bindings covered by this ticket.
 However, in order to do this we need to find a way to encode the fact that
 the bindings are generated.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11051#comment:3>
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