Refactor, improve, and document the deriving mechanism

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

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index 93229d3..63b73fc 100644 (file)
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -635,30 +635,20 @@ iDFunId info = instanceDFunId (iSpec info)
 
 data InstBindings
   = VanillaInst                -- The normal case
-       (LHsBinds Name)         -- Bindings
+       (LHsBinds Name)         -- Bindings for the instance methods
        [LSig Name]             -- User pragmas recorded for generating 
                                -- specialised instances
 
   | 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 (VanillaInst b _) = pprLHsBinds b
+    details NewTypeDerived    = text "Derived from the representation type"
 
 simpleInstInfoClsTy :: InstInfo -> (Class, Type)
 simpleInstInfoClsTy info = case instanceHead (iSpec info) of