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Recusive superclass epansion is over-keen

    • Closed Issue created by Simon Peyton Jones @simonpj

    Consider this, with RecursiveSuperClasses:

    class C a => D a where
  cop :: a -> a

class D a => C a where
  dop :: a -> a

g :: C a => a -> Bool
g x = g x

f :: C a => a -> Bool
f x = g x

    When we compile this we get

    f = \ (@ a_aXf) ($dC_aXh :: C a_aXf) (eta_B1 :: a_aXf) ->
      g @ a_aXf (Foo.$p1D @ a_aXf (Foo.$p1C @ a_aXf $dC_aXh)) eta_B1

    Notice the ridiculous double superclass selection from $dC_aXh. It's not wrong, just stupid!

    Trac metadata
    Trac field Value
    Version 8.2.2
    Type Bug
    TypeOfFailure OtherFailure
    Priority normal
    Resolution Unresolved
    Component Compiler
    Test case
    Differential revisions
    BlockedBy
    Related
    Blocking
    CC
    Operating system
    Architecture
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