Revise implementation of overlapping type family instances.

This commit changes the syntax and story around overlapping type
family instances. Before, we had "unbranched" instances and
"branched" instances. Now, we have closed type families and
open ones.

The behavior of open families is completely unchanged. In particular,
coincident overlap of open type family instances still works, despite
emails to the contrary.

A closed type family is declared like this:
> type family F a where
>   F Int = Bool
>   F a   = Char
The equations are tried in order, from top to bottom, subject to
certain constraints, as described in the user manual. It is not
allowed to declare an instance of a closed family.

1 files changed, 1 insertions, 5 deletions

diff --git a/compiler/vectorise/Vectorise/Utils/Base.hs b/compiler/vectorise/Vectorise/Utils/Base.hs
index d088f45355..0bd54f4408 100644
--- a/compiler/vectorise/Vectorise/Utils/Base.hs
+++ b/compiler/vectorise/Vectorise/Utils/Base.hs
@@ -39,8 +39,6 @@ import DataCon
 import MkId
 import DynFlags
 import FastString
-import Util
-import Panic
 
 #include "HsVersions.h"
 
@@ -211,10 +209,8 @@ pdataReprTyCon :: Type -> VM (TyCon, [Type])
 pdataReprTyCon ty 
   = do 
     { FamInstMatch { fim_instance = famInst
-                   , fim_index    = index
                    , fim_tys      = tys } <- builtin pdataTyCon >>= (`lookupFamInst` [ty])
-    ; ASSERT( index == 0 )
-      return (dataFamInstRepTyCon famInst, tys)
+    ; return (dataFamInstRepTyCon famInst, tys)
     }
 
 -- |Get the representation tycon of the 'PData' data family for a given type constructor.