[GHC] #10589: Core Lint error with LambdaCase

29 Jun 2015

      #10589: Core Lint error with LambdaCase
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              Reporter:  goldfire    |             Owner:  goldfire
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.1
  (Type checker)                     |  Operating System:  Unknown/Multiple
              Keywords:              |   Type of failure:  None/Unknown
          Architecture:              |        Blocked By:
  Unknown/Multiple                   |   Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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 When I say

 {{{
 {-# LANGUAGE LambdaCase, TypeFamilies #-}

 type family F a where
   F a = Bool -> a

 foo = (\case True -> 5
              False -> 6) :: F Int
 }}}

 `-dcore-lint` tells me

 {{{
 *** Core Lint errors : in result of Desugar (after optimization) ***
 /Users/rae/temp/Bug.hs:6:1: Warning:
     [RHS of foo :: Bool -> Int]
     From-type of Cast differs from type of enclosed expression
 ...
 }}}

 The problem is a missing `mkTcSymCo` in the relevant bit of `tcExpr`.

 Will fix in ongoing work.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10589
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