[GHC] #8906: rewrite arrow form in type signature sometimes leads to exception, sometimes not

[GHC]

#8906: rewrite arrow form in type signature sometimes leads to exception,
sometimes not
----------------------------------+---------------------------------
       Reporter:  thaumkid        |             Owner:
           Type:  bug             |            Status:  new
       Priority:  low             |         Milestone:
      Component:  GHCi            |           Version:  7.6.3
       Keywords:                  |  Operating System:  Windows
   Architecture:  x86_64 (amd64)  |   Type of failure:  None/Unknown
     Difficulty:  Unknown         |         Test Case:
     Blocked By:                  |          Blocking:
Related Tickets:                  |
----------------------------------+---------------------------------
 Seems like the arrow form in signatures should either be restricted
 further or made more flexible.

 {{{
 > let a = id :: ((->) a) a
 > a 2
 *** Exception: expectJust cpeBody:collect_args
 > :t a
 a :: (->) a a
 }}}

 {{{
 > let a = id :: (->) a a
 > a 2
 2
 > :t a
 a :: a -> a
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8906>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler