[GHC] #5633: TypeFamilies don't seem to play with LIberalTypeSynonyms

[GHC]

#5633: TypeFamilies don't seem to play with LIberalTypeSynonyms
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  Reporter:  ocharles                   |          Owner:                                  
      Type:  bug                        |         Status:  closed                          
  Priority:  normal                     |      Milestone:                                  
 Component:  Compiler                   |        Version:  7.0.4                           
Resolution:  invalid                    |       Keywords:  TypeFamilies LiberalTypeSynonyms
  Testcase:                             |      Blockedby:                                  
Difficulty:                             |             Os:  Linux                           
  Blocking:                             |   Architecture:  x86                             
   Failure:  GHC rejects valid program  |  
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Comment(by ocharles):

 Hi simon, thanks for the explanation.

 It's a shame that it can't work, as a newtype doesn't really cut it. Fwiw,
 the motivation of this ticket came from trying to abstract away Record
 declarations in HaskellDB with code that also uses type families.

 HaskellDB uses either `RecCons FieldType (Expr RetType)` or `RecCons
 FieldType RetType` depending on how a record is used/returned, and there
 doesn't seem to be a way to capture this with a type family, where I was
 trying to abstract Expr :: * -> * away. However, this ticket isn't the
 right place for that discussion, so I'll move that to a mailing list :)

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5633#comment:2>
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