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When I say

{-# LANGUAGE TemplateHaskell, TypeFamilies #-}
{-# OPTIONS_GHC -ddump-splices -dsuppress-uniques #-}

module Bug where

$([d| class C a where
        type F a
        type F a = a |])

I get

    [d| class C a where
          type family F a
          F a = a |]
  ======>

Bug.hs:6:7: Warning:
    Cannot desugar this Template Haskell declaration:
        class C a where
          type family F a
          F a = a

There are two problems here:

1. This really should work.
2. The pretty-printer here omits the type on the default definition for F. (The word family is optional there, but isn't actually wrong.)

Trac metadata

Trac field	Value
Version	7.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
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