[GHC] #13898: Consolidate treatment of strictness in parser

[GHC]

#13898: Consolidate treatment of strictness in parser
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           Reporter:  bgamari        |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:  8.4.1
          Component:  Compiler       |           Version:  8.0.1
  (Parser)                           |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Currently GHC's treatment of binding strictness in the Haskell parser and
 AST is the result of a long, winding evolution. Since Phab:D3670 we have
 tracked strictness of variable bindings (e.g. `!x = ...`) in the
 `SrcStrictness` in `FunRhs` (see `Note [Varieties of bindings]`). This is
 parsed by ``. However, explicitly lazy bindings (e.g. `~x = ...`) are
 parsed via a completely different means (see the rule starting with `~` in
 `aexp`) and represented as `ELazyPat` until being mangled into a pattern
 in `RdrHsSyn`. It seems to me like these two paths should be more
 symmetric.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13898>
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