[GHC] #7880: Require "forall" in definitions of polymorphic types

[GHC]

#7880: Require "forall" in definitions of polymorphic types
---------------------------------+------------------------------------------
    Reporter:  monoidal          |       Owner:                             
        Type:  bug               |      Status:  new                        
    Priority:  normal            |   Milestone:                             
   Component:  Compiler          |     Version:  7.6.3                      
    Keywords:                    |          Os:  Unknown/Multiple           
Architecture:  Unknown/Multiple  |     Failure:  GHC accepts invalid program
  Difficulty:  Unknown           |    Testcase:                             
   Blockedby:                    |    Blocking:                             
     Related:                    |  
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Comment(by simonpj):

 I have some sympathy with this, but what about
 {{{
 f :: (Num a => a -> a) -> Int
 }}}
 Which of these does it mean?
 {{{
 f :: (forall a. Num a => a -> a) -> Int
 f :: forall a. (Num a => a -> a) -> Int
 }}}
 Your proposal is (in effect) that "=>" does not trigger an implicit
 "forall"; only the top level of a type does that.  I think that's probably
 very sensible, but it's a breaking change, and I don't know how much code,
 if any, would break.

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7880#comment:2>
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