[GHC] #12640: Class member functions not substituted for MultiParamTypeClasses

28 Sep 2016


      #12640: Class member functions not substituted for MultiParamTypeClasses
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           Reporter:  jeremy-list    |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Runtime
  Unknown/Multiple                   |  performance bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 When the following code is compiled with "-O2 -ddump-rule-firings" the
 rule is not fired: presumably because the simplifier does not recognize
 that (+++) = ex_or.
 {{{#!hs
 {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies #-}
 class Ex2 a b c | a b -> c where
   (+++) :: a -> b -> c

 instance Ex2 Bool Bool Bool where
   (+++) = ex_or

 {-# INLINE [2] ex_or #-}
 ex_or = (||)

 {-# RULES
 "force-inline" forall a b . ex_or a b = a || b
  #-}

 main = print (True +++ True)
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12640
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