[GHC] #4359: Implement lambda-case/lambda-if

[GHC]

#4359: Implement lambda-case/lambda-if
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  Reporter:  batterseapower    |          Owner:                  
      Type:  feature request   |         Status:  new             
  Priority:  normal            |      Milestone:  7.6.1           
 Component:  Compiler          |        Version:  7.1             
Resolution:                    |       Keywords:                  
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown      |     Difficulty:  Unknown         
  Testcase:                    |      Blockedby:                  
  Blocking:                    |        Related:                  
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Comment(by simonmar):

 I think it would be a mistake to treat `\case` as a single lexeme, because
 it doesn't fit at all well with the way the lexical syntax is presented in
 the Haskell report.

 I think it might be better to implement `\case` using a lexer state rather
 than tracking the previous token in the monad as the patch currently does.
 But it's hard to say for sure without trying it.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4359#comment:72>
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