[project @ 2000-11-20 14:48:52 by simonpj]

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

diff --git a/ghc/compiler/typecheck/TcInstDcls.lhs b/ghc/compiler/typecheck/TcInstDcls.lhs
index ca18b67..841988d 100644 (file)
--- a/ghc/compiler/typecheck/TcInstDcls.lhs
+++ b/ghc/compiler/typecheck/TcInstDcls.lhs
@@ -56,7 +56,7 @@ import PprType                ( pprConstraint, pprPred )
 import TyCon           ( TyCon, isSynTyCon )
 import Type            ( splitDFunTy, isTyVarTy,
                          splitTyConApp_maybe, splitDictTy,
-                         splitAlgTyConApp_maybe, splitForAllTys,
+                         splitForAllTys,
                          tyVarsOfTypes, mkClassPred, mkTyVarTy,
                          getClassTys_maybe
                        )
@@ -167,11 +167,10 @@ tcInstDecls1 :: PackageInstEnv
             -> TcEnv                   -- Contains IdInfo for dfun ids
             -> (Name -> Maybe Fixity)  -- for deriving Show and Read
             -> Module                  -- Module for deriving
-            -> [TyCon]
             -> [RenamedHsDecl]
             -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
 
-tcInstDecls1 inst_env0 prs hst unf_env get_fixity mod tycons decls
+tcInstDecls1 inst_env0 prs hst unf_env get_fixity mod decls
   = let
        inst_decls = [inst_decl | InstD inst_decl <- decls]     
        tycl_decls = [decl      | TyClD decl <- decls]
@@ -580,7 +579,7 @@ tcInstDecl2 (InstInfo { iLocal = is_local, iDFunId = dfun_id,
         methods_lie = plusLIEs insts_needed_s
     in
 
-       -- Ditto method bindings
+       -- Simplify the constraints from methods
     tcAddErrCtxt methodCtxt (
       tcSimplifyAndCheck
                 (ptext SLIT("instance declaration context"))
@@ -589,11 +588,9 @@ tcInstDecl2 (InstInfo { iLocal = is_local, iDFunId = dfun_id,
                 methods_lie
     )                                           `thenTc` \ (const_lie1, lie_binds1) ->
     
-       -- Now do the simplification again, this time to get the
-       -- bindings; this time we use an enhanced "avails"
-       -- Ignore errors because they come from the *previous* tcSimplify
-    discardErrsTc (
-       tcSimplifyAndCheck
+       -- Figure out bindings for the superclass context
+    tcAddErrCtxt superClassCtxt (
+      tcSimplifyAndCheck
                 (ptext SLIT("instance declaration context"))
                 inst_tyvars_set
                 dfun_arg_dicts         -- NB! Don't include this_dict here, else the sc_dicts
@@ -725,11 +722,6 @@ scrutiniseInstanceHead clas inst_taus
     maybe_tycon_app      = splitTyConApp_maybe first_inst_tau
     Just (tycon, arg_tys) = maybe_tycon_app
 
-       -- Stuff for an *algebraic* data type
-    alg_tycon_app_maybe           = splitAlgTyConApp_maybe first_inst_tau
-                               -- The "Alg" part looks through synonyms
-    Just (alg_tycon, _, _) = alg_tycon_app_maybe
- 
     ccallable_type   dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
     creturnable_type        ty = isFFIResultTy ty
 \end{code}
@@ -793,6 +785,5 @@ nonBoxedPrimCCallErr clas inst_ty
                        ppr inst_ty])
 
 methodCtxt     = ptext SLIT("When checking the methods of an instance declaration")
+superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")
 \end{code}
-
-