[GHC] #14691: Replace EvTerm with CoreExpr

[GHC]

#14691: Replace EvTerm with CoreExpr
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        Reporter:  nomeata           |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.3
  checker)                           |
      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 nomeata):

 Prelimary work in `wip/14691`.

 But here is slight refactoring annoyance: The code from `dsEvTerm` would
 have to move into the new smart constructors, e.g. `evTypeable`, which
 replaces `EvTypable`. But the former is monadic (in `DsM`, to lookup
 things), while the latter is pure. So the uses of these smart constructors
 need to be made monadic. It seems to affect  `evTypeable`, `evCallStack`
 and `evLit`, it looks like the other smart constructors can remain pure.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14691#comment:3>
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