[GHC] #8477: Allow inferring ambiguous types

[GHC]

#8477: Allow inferring ambiguous types
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        Reporter:  aavogt            |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.6.3
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  8390
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Comment (by simonpj):

 Like I say, I'm doubtful about allowing functions to get ambiguous
 ''inferred'' types, because that plants hidden land mines for those who
 call the function. If you give a signature, you are explicitly asking for
 this particular land mine. If you want it to have an ambiguous type, say
 so!  It's like a per-declaration pragma, if you like.

 It would not be impossible to make `-XAllowAmbiguousTypes` work for
 inferred types, but actually it would not be entirely straightforward; see
 `Note [Impedence matching]` in `TcBinds`.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8477#comment:6>
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