Fix a bug in MatchCon, and clarify what dataConInstOrigArgTys does

[ghc-hetmet.git] / compiler / basicTypes / DataCon.lhs

diff --git a/compiler/basicTypes/DataCon.lhs b/compiler/basicTypes/DataCon.lhs
index 550be30..9ce966e 100644 (file)
--- a/compiler/basicTypes/DataCon.lhs
+++ b/compiler/basicTypes/DataCon.lhs
@@ -640,34 +640,37 @@ dataConUserType  (MkData { dcUnivTyVars = univ_tvs,
     mkFunTys arg_tys $
     res_ty
 
-dataConInstArgTys :: DataCon
+dataConInstArgTys :: DataCon   -- A datacon with no existentials or equality constraints
+                               -- However, it can have a dcTheta (notably it can be a 
+                               -- class dictionary, with superclasses)
                  -> [Type]     -- Instantiated at these types
-                               -- NB: these INCLUDE the existentially quantified arg types
                  -> [Type]     -- Needs arguments of these types
-                               -- NB: these INCLUDE the existentially quantified dict args
+                               -- NB: these INCLUDE any dict args
                                --     but EXCLUDE the data-decl context which is discarded
                                -- It's all post-flattening etc; this is a representation type
-dataConInstArgTys dc@(MkData {dcRepArgTys = arg_tys, 
-                             dcUnivTyVars = univ_tvs, 
+dataConInstArgTys dc@(MkData {dcRepArgTys = rep_arg_tys, 
+                             dcUnivTyVars = univ_tvs, dcEqSpec = eq_spec,
                              dcExTyVars = ex_tvs}) inst_tys
- = ASSERT2 ( length tyvars == length inst_tys 
-           , ptext SLIT("dataConInstArgTys") <+> ppr dc $$ ppr tyvars $$ ppr inst_tys)
-           
-   map (substTyWith tyvars inst_tys) arg_tys
- where
-   tyvars = univ_tvs ++ ex_tvs
-
-
--- And the same deal for the original arg tys
-dataConInstOrigArgTys :: DataCon -> [Type] -> [Type]
+ = ASSERT2 ( length univ_tvs == length inst_tys 
+           , ptext SLIT("dataConInstArgTys") <+> ppr dc $$ ppr univ_tvs $$ ppr inst_tys)
+   ASSERT2 ( null ex_tvs && null eq_spec, ppr dc )        
+   map (substTyWith univ_tvs inst_tys) rep_arg_tys
+
+dataConInstOrigArgTys 
+       :: DataCon      -- Works for any DataCon
+       -> [Type]       -- Includes existential tyvar args, but NOT
+                       -- equality constraints or dicts
+       -> [Type]       -- Returns just the instsantiated *value* arguments
+-- For vanilla datacons, it's all quite straightforward
+-- But for the call in MatchCon, we really do want just the value args
 dataConInstOrigArgTys dc@(MkData {dcOrigArgTys = arg_tys,
                                  dcUnivTyVars = univ_tvs, 
                                  dcExTyVars = ex_tvs}) inst_tys
- = ASSERT2( length tyvars == length inst_tys
+  = ASSERT2( length tyvars == length inst_tys
           , ptext SLIT("dataConInstOrigArgTys") <+> ppr dc $$ ppr tyvars $$ ppr inst_tys )
-   map (substTyWith tyvars inst_tys) arg_tys
- where
-   tyvars = univ_tvs ++ ex_tvs
+    map (substTyWith tyvars inst_tys) arg_tys
+  where
+    tyvars = univ_tvs ++ ex_tvs
 \end{code}
 
 These two functions get the real argument types of the constructor,