[GHC] #7010: Type error in one function causes wrong type error report in another function when using type families

[GHC]

#7010: Type error in one function causes wrong type error report in another
function when using type families
------------------------------------------------+---------------------------
  Reporter:  Lemming                            |          Owner:                  
      Type:  bug                                |         Status:  closed          
  Priority:  low                                |      Milestone:  7.6.1           
 Component:  Compiler                           |        Version:  7.4.1           
Resolution:  fixed                              |       Keywords:                  
        Os:  Unknown/Multiple                   |   Architecture:  Unknown/Multiple
   Failure:  Incorrect warning at compile-time  |     Difficulty:  Unknown         
  Testcase:  indexed-types/should_fail/T7010    |      Blockedby:                  
  Blocking:                                     |        Related:                  
------------------------------------------------+---------------------------
Changes (by simonpj):

  * status:  new => closed
  * testcase:  => indexed-types/should_fail/T7010
  * resolution:  => fixed


Comment:

 Recent changes in the type inference engine mean that you now get just one
 error, and it's on `filterFormats`, as it should be
 {{{
 T7010.hs:44:27:
     Couldn't match type `Serial (ValueTuple Float)' with `IO Float'
     Expected type: (Float, ValueTuple Vector)
       Actual type: (Float, ValueTuple Float)
     In the first argument of `withArgs', namely `plug'
     In the expression: withArgs plug
     In an equation for `filterFormants': filterFormants = withArgs plug
 }}}
  To be honest I'm not 100% certain of why this has come right, and that
 means I'm not certain that the solution is robust (mabye it's a fluke).
 But I'm sort of time, so I'm closing the ticket. But I'm adding the test
 as a regression test so we'll know immediately if it stops working.

 Thanks for the example.

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7010#comment:2>
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