[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 nomeata):

 Oh, and fun fact: It might be possible to remove `App` completely and
 replace it with a pattern synonym here: Due to `compressArgs ty [x] =
 [x]`, `Apps f 1 [e]` is equivalent to `App f e`.

 So this might not actually be a serious change to core, nor might it be
 increasing the number of constructors: Using a bidirectional smart
 constructor (which does optimizes the representation under the hood) this
 can hopefully be a completely transparent optimization of the
 representation.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12618#comment:10>
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