In tcSplittyConApp_maybe, add the PredTy case

[ghc-hetmet.git] / compiler / typecheck / TcEnv.lhs

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index 7828394..6e5f381 100644 (file)
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -50,8 +50,8 @@ import TcIface                ( tcImportDecl )
 import IfaceEnv                ( newGlobalBinder )
 import TcRnMonad
 import TcMType         ( zonkTcType, zonkTcTyVarsAndFV )
-import TcType          ( Type, TcKind, TcTyVar, TcTyVarSet, TcType, 
-                         substTy, tyVarsOfType, tcTyVarsOfTypes, mkTyConApp,
+import TcType          ( Type, TcKind, TcTyVar, TcTyVarSet, TcType, PredType,
+                         tyVarsOfType, tcTyVarsOfTypes, mkTyConApp,
                          getDFunTyKey, tcTyConAppTyCon, tcGetTyVar, mkTyVarTy,
                          tidyOpenType, isRefineableTy
                        )
@@ -362,7 +362,7 @@ findGlobals tvs tidy_env
          Just d  -> go tidy_env1 (d:acc) things
          Nothing -> go tidy_env1 acc     things
 
-    ignore_it ty = not (tvs `intersectsVarSet` tyVarsOfType ty)
+    ignore_it ty = tvs `disjointVarSet` tyVarsOfType ty
 
 -----------------------
 find_thing ignore_it tidy_env (ATcId { tct_id = id })
@@ -567,20 +567,26 @@ data InstBindings
        [LSig Name]             -- User pragmas recorded for generating 
                                -- specialised instances
 
-  | NewTypeDerived             
-        TyCon                   -- tycon for the newtype
-                                -- Used for deriving instances of newtypes, where the
-       [Type]                  -- witness dictionary is identical to the argument 
-                               -- dictionary.  Hence no bindings, no pragmas
-       -- The [Type] are the representation types
-       -- See notes in TcDeriv
+  | NewTypeDerived              -- Used for deriving instances of newtypes, where the
+                               -- witness dictionary is identical to the argument 
+                               -- dictionary.  Hence no bindings, no pragmas.
+       (Maybe [PredType])
+               -- Nothing      => The newtype-derived instance involves type variables,
+               --                 and the dfun has a type like df :: forall a. Eq a => Eq (T a)
+               -- Just (r:scs) => The newtype-defined instance has no type variables
+               --                 so the dfun is just a constant, df :: Eq T
+               --                 In this case we need to know waht the rep dict, r, and the 
+               --                 superclasses, scs, are.  (In the Nothing case these are in the
+               --                 dict fun's type.)
+               --                 Invariant: these PredTypes have no free variables
+               -- NB: In both cases, the representation dict is the *first* dict.
 
 pprInstInfo info = vcat [ptext SLIT("InstInfo:") <+> ppr (idType (iDFunId info))]
 
 pprInstInfoDetails info = pprInstInfo info $$ nest 2 (details (iBinds info))
   where
     details (VanillaInst b _)  = pprLHsBinds b
-    details (NewTypeDerived _  _) = text "Derived from the representation type"
+    details (NewTypeDerived _) = text "Derived from the representation type"
 
 simpleInstInfoClsTy :: InstInfo -> (Class, Type)
 simpleInstInfoClsTy info = case instanceHead (iSpec info) of