[GHC] #12618: Add saturated constructor applications to Core

[GHC]

#12618: Add saturated constructor applications to Core
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        Reporter:  simonpj           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      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 lukemaurer):

 We went back and forth with something like this in Sequent Core, where
 having the dual of Case was nice. One downside hasn't been mentioned,
 though: We'll need to use smart constructors more consistently, or
 otherwise not be able to count on ''all'' saturated constructor
 applications to use `ConApp`. Currently there's `mkCoreApp` and
 `mkCoreApps`, but those are only necessary when the let/app invariant must
 be enforced; IIRC, lots of places where let/app is known to hold just use
 fold `App` over the arguments.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12618#comment:20>
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