[GHC] #8207: Show instance for Language in DynFlags

[GHC]

#8207: Show instance for Language in DynFlags
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       Reporter:  Fuuzetsu          |             Owner:
           Type:  feature request   |            Status:  new
       Priority:  low               |         Milestone:
      Component:  GHC API           |           Version:  7.7
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 I feel that the GHC API could benefit from a Show instance for Language in
 DynFlags.hs.

 Currently, if we want to display the language being used we have to do
 something like

 {{{
           foo inf = case hmi_language inf of
             Nothing -> Nothing
             Just Haskell98 -> Just "Haskell98"
             Just Haskell2010 -> Just "Haskell2010"
 }}}

 This is pretty much just the Show instance (over Maybe) and Haskell can
 derive it for us automatically: we just need to change `deriving Enum` to
 `deriving (Enum, Show)`. The above solution is not the most robust ever as
 if this data type is ever changed, this starts to form an incomplete
 pattern. If we have a catch all `_`, GHC complains about overlapping
 patterns. Easily solved with `show <$> hmi_language inf`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8207>
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