[GHC] #9388: Narrow the scope of the notorious "state hack"

[GHC]

#9388: Narrow the scope of the notorious "state hack"
-------------------------------------+-------------------------------------
        Reporter:  simonpj           |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.8.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by nomeata):

 I’m considering giving this one shot (pun intended), and I’m reading the
 current implementation of the state hack, and found some pretty old-dated
 comments, including this one from 2004 in `Id.hs`:
 {{{
        -- Another good example is in fill_in in PrelPack.lhs.  We should
 be able to
        -- spot that fill_in has arity 2 (and when Keith is done, we will)
 but we can't yet.
 }}}
 I do not know who Keith is, and why that would help, and most likely
 something about todays demand analyzer should be written there. Simon, if
 you have a minute, would you mind revisiting the comment at `isStateHack`?
 It would help whoever tackles the problem next. Thanks!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9388#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler