FIX #3272

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

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index d038845..36231cd 100644 (file)
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -57,6 +57,7 @@ import TcType
 -- import TcSuspension
 import qualified Type
 import Id
+import Coercion
 import Var
 import VarSet
 import VarEnv
@@ -69,11 +70,9 @@ import TypeRep
 import Class
 import Name
 import NameEnv
-import OccName
 import HscTypes
 import SrcLoc
 import Outputable
-import Maybes
 import Unique
 import FastString
 \end{code}
@@ -125,11 +124,8 @@ tcLookupGlobal name
        }}}}}
 
 tcLookupField :: Name -> TcM Id                -- Returns the selector Id
-tcLookupField name = do
-    thing <- tcLookup name     -- Note [Record field lookup]
-    case thing of
-       AGlobal (AnId id) -> return id
-       thing -> wrongThingErr "field name" thing name
+tcLookupField name 
+  = tcLookupId name    -- Note [Record field lookup]
 
 {- Note [Record field lookup]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -175,9 +171,13 @@ tcLookupLocatedTyCon = addLocM tcLookupTyCon
 
 -- Look up the instance tycon of a family instance.
 --
--- The match must be unique - ie, match exactly one instance - but the 
--- type arguments used for matching may be more specific than those of 
--- the family instance declaration.
+-- The match may be ambiguous (as we know that overlapping instances have
+-- identical right-hand sides under overlapping substitutions - see
+-- 'FamInstEnv.lookupFamInstEnvConflicts').  However, the type arguments used
+-- for matching must be equal to or be more specific than those of the family
+-- instance declaration.  We pick one of the matches in case of ambiguity; as
+-- the right-hand sides are identical under the match substitution, the choice
+-- does not matter.
 --
 -- Return the instance tycon and its type instance.  For example, if we have
 --
@@ -198,12 +198,17 @@ tcLookupFamInst tycon tys
        ; eps <- getEps
        ; let instEnv = (eps_fam_inst_env eps, tcg_fam_inst_env env)
        ; case lookupFamInstEnv instEnv tycon tys of
-          [(fam_inst, rep_tys)] -> return $ Just (famInstTyCon fam_inst, 
-                                                   rep_tys)
-          _                     -> return Nothing
+          []                      -> return Nothing
+          ((fam_inst, rep_tys):_) 
+             -> return $ Just (famInstTyCon fam_inst, rep_tys)
        }
 \end{code}
 
+\begin{code}
+instance MonadThings (IOEnv (Env TcGblEnv TcLclEnv)) where
+    lookupThing = tcLookupGlobal
+\end{code}
+
 %************************************************************************
 %*                                                                     *
                Extending the global environment
@@ -522,13 +527,13 @@ tcExtendRules lcl_rules thing_inside
 
 \begin{code}
 instance Outputable ThStage where
-   ppr Comp         = text "Comp"
+   ppr (Comp l)             = text "Comp" <+> int l
    ppr (Brack l _ _) = text "Brack" <+> int l
    ppr (Splice l)    = text "Splice" <+> int l
 
 
 thLevel :: ThStage -> ThLevel
-thLevel Comp         = topLevel
+thLevel (Comp l)      = l
 thLevel (Splice l)    = l
 thLevel (Brack l _ _) = l
 
@@ -544,7 +549,7 @@ checkWellStaged pp_thing bind_lvl use_stage
   | bind_lvl == topLevel       -- GHC restriction on top level splices
   = failWithTc $ 
     sep [ptext (sLit "GHC stage restriction:") <+>  pp_thing,
-        nest 2 (ptext (sLit "is used in a top-level splice, and must be imported, not defined locally"))]
+        nest 2 (ptext (sLit "is used in") <+> use_lvl_doc <> ptext (sLit ", and must be imported, not defined locally"))]
 
   | otherwise                  -- Badly staged
   = failWithTc $               -- E.g.  \x -> $(f x)
@@ -553,7 +558,9 @@ checkWellStaged pp_thing bind_lvl use_stage
                ptext (sLit "but used at stage") <+> ppr use_lvl]
   where
     use_lvl = thLevel use_stage
-
+    use_lvl_doc | use_lvl == thLevel topStage    = ptext (sLit "a top-level splice")
+                | use_lvl == thLevel topAnnStage = ptext (sLit "an annotation")
+                | otherwise                      = panic "checkWellStaged"
 
 topIdLvl :: Id -> ThLevel
 -- Globals may either be imported, or may be from an earlier "chunk" 
@@ -635,8 +642,12 @@ data InstBindings a
                                -- specialised instances
 
   | NewTypeDerived              -- Used for deriving instances of newtypes, where the
-                               -- witness dictionary is identical to the argument 
+       CoercionI               -- witness dictionary is identical to the argument 
                                -- dictionary.  Hence no bindings, no pragmas.
+               -- The coercion maps from newtype to the representation type
+               -- (mentioning type variables bound by the forall'd iSpec variables)
+               -- E.g.   newtype instance N [a] = N1 (Tree a)
+               --        co : N [a] ~ Tree a
 
 pprInstInfo :: InstInfo a -> SDoc
 pprInstInfo info = vcat [ptext (sLit "InstInfo:") <+> ppr (idType (iDFunId info))]
@@ -644,8 +655,8 @@ pprInstInfo info = vcat [ptext (sLit "InstInfo:") <+> ppr (idType (iDFunId info)
 pprInstInfoDetails :: OutputableBndr a => InstInfo a -> SDoc
 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 a -> (Class, Type)
 simpleInstInfoClsTy info = case instanceHead (iSpec info) of