[GHC] #5248: Infer type context in a type signature

[GHC]

#5248: Infer type context in a type signature
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    Reporter:  gidyn                    |        Owner:                           
        Type:  feature request          |       Status:  new                      
    Priority:  normal                   |    Milestone:                           
   Component:  Compiler (Type checker)  |      Version:  7.0.3                    
    Keywords:                           |     Testcase:                           
   Blockedby:                           |   Difficulty:                           
          Os:  Unknown/Multiple         |     Blocking:                           
Architecture:  Unknown/Multiple         |      Failure:  GHC rejects valid program
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Comment(by gidyn):

 I'm not sure what you mean by "that's the way Haskell is"; many GHC
 features go beyond the Haskell standard.

 Perhaps I misworded the ticket, as I wasn't referring to inferring type
 contexts from a method's implementation. The type context given in a data-
 type's definition should be available wherever the data type is used, so
 the (...) => syntax shouldn't be necessary for this case.

 To put the issue differently: A type variable in a data/type constructor
 is restricted to a given type class. Currently, this restriction has to be
 repeated in the signature of every function that uses the restriction.
 This repetition is superfluous noise, which is required by the compiler,
 but adds no information.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5248#comment:2>
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