[GHC] #16119: Hide the gnarly levity polymorphism stuff in the signatures of `undefined`, `throw`, etc

[GHC]

#16119: Hide the gnarly levity polymorphism stuff in the signatures of `undefined`,
`throw`, etc
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        Reporter:  jberryman         |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  libraries/base    |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by harpocrates):

 This is gonna be easily fixable once Hi Haddock lands. See
 https://github.com/haskell/haddock/pull/941 in particular. There's going
 to be a module-level Haddock option for controlling whether levity
 polymorphic signatures in that module get defaulted or not.

 If we want `throw :: Exception e => e -> a`, we'll have to add `{-#
 OPTIONS_HADDOCK print-runtime-reps #-}` to the top of
 `Control.Exception.Base`.

 Personally, I'd lean towards leaving the `throw`'s levity polymorphic
 signature in `Control.Exception.Base` and defaulting the re-export in
 `Control.Exception`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16119#comment:1>
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