Desugared:
{- plain CoRec -}
dfun.Eq.Test.Foo :: <Eq Test.Foo>
dfun.Eq.Test.Foo =
    let
      ==.76 =
	  \ ds.83 ds.84 ->
	      let
		fail.85 =
		    (error Bool)
			"\"ds027.hs\", line 8: pattern-matching failure [function binding]\n"S
	      in 
		case ds.83 of {
		  Test.Bar ->
		      case ds.84 of {
			Test.Baz -> True
			_ ->  fail.85
		      }
		  _ ->  fail.85
		} in
    let
      /=.77 =
	  \ ds.89 ds.90 ->
	      let
		fail.91 =
		    (error Bool)
			"\"ds027.hs\", line 9: pattern-matching failure [function binding]\n"S
	      in 
		case ds.89 of {
		  Test.Bar ->
		      case ds.90 of {
			Test.Baz -> False
			_ ->  fail.91
		      }
		  _ ->  fail.91
		}
    in 
      MkTuple2!
	  (Test.Foo -> Test.Foo -> Bool)
	  (Test.Foo -> Test.Foo -> Bool)
	  ==.76
	  /=.77
{- end plain CoRec -}