[project @ 2005-02-25 13:06:31 by simonpj]

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

diff --git a/ghc/compiler/typecheck/Inst.lhs b/ghc/compiler/typecheck/Inst.lhs
index 4fb3f87..f75d1d3 100644 (file)
--- a/ghc/compiler/typecheck/Inst.lhs
+++ b/ghc/compiler/typecheck/Inst.lhs
@@ -50,11 +50,11 @@ import TcRnMonad
 import TcEnv   ( tcLookupId, checkWellStaged, topIdLvl, tcMetaTy )
 import InstEnv ( DFunId, InstEnv, lookupInstEnv, checkFunDeps, extendInstEnv )
 import TcIface ( loadImportedInsts )
-import TcMType ( zonkTcType, zonkTcTypes, zonkTcPredType, 
-                 zonkTcThetaType, tcInstTyVar, tcInstType
+import TcMType ( zonkTcType, zonkTcTypes, zonkTcPredType, zonkTcThetaType, 
+                 tcInstTyVar, tcInstType, tcSkolType
                )
 import TcType  ( Type, TcType, TcThetaType, TcTyVarSet, TcTyVar, TcPredType,
-                 PredType(..), typeKind, mkSigmaTy,
+                 PredType(..), SkolemInfo(..), typeKind, mkSigmaTy,
                  tcSplitForAllTys, tcSplitForAllTys, 
                  tcSplitPhiTy, tcIsTyVarTy, tcSplitDFunTy, tcSplitDFunHead,
                  isIntTy,isFloatTy, isIntegerTy, isDoubleTy,
@@ -71,27 +71,25 @@ import Type ( TvSubst, substTy, substTyVar, substTyWith, substTheta, zipTopTvSub
 import Unify   ( tcMatchTys )
 import Kind    ( isSubKind )
 import Packages        ( isHomeModule )
-import HscTypes        ( HscEnv( hsc_HPT ), ExternalPackageState(..), 
-                 ModDetails( md_insts ), HomeModInfo( hm_details )  )
+import HscTypes        ( ExternalPackageState(..) )
 import CoreFVs ( idFreeTyVars )
 import DataCon ( DataCon, dataConTyVars, dataConStupidTheta, dataConName )
 import Id      ( Id, idName, idType, mkUserLocal, mkLocalId )
 import PrelInfo        ( isStandardClass, isNoDictClass )
 import Name    ( Name, mkMethodOcc, getOccName, getSrcLoc, nameModule,
-                 isInternalName, setNameUnique, mkSystemNameEncoded )
+                 isInternalName, setNameUnique, mkSystemVarNameEncoded )
 import NameSet ( addOneToNameSet )
 import Literal ( inIntRange )
 import Var     ( TyVar, tyVarKind, setIdType )
 import VarEnv  ( TidyEnv, emptyTidyEnv )
 import VarSet  ( elemVarSet, emptyVarSet, unionVarSet, mkVarSet )
-import Module  ( moduleEnvElts, elemModuleEnv, lookupModuleEnv )
 import TysWiredIn ( floatDataCon, doubleDataCon )
 import PrelNames       ( integerTyConName, fromIntegerName, fromRationalName, rationalTyConName )
 import BasicTypes( IPName(..), mapIPName, ipNameName )
 import UniqSupply( uniqsFromSupply )
 import SrcLoc  ( mkSrcSpan, noLoc, unLoc, Located(..) )
 import CmdLineOpts( DynFlags )
-import Maybes  ( isJust, fromJust )
+import Maybes  ( isJust )
 import Outputable
 \end{code}
 
@@ -402,7 +400,7 @@ newLitInst orig lit expected_ty
   = getInstLoc orig            `thenM` \ loc ->
     newUnique                  `thenM` \ new_uniq ->
     let
-       lit_nm   = mkSystemNameEncoded new_uniq FSLIT("lit")
+       lit_nm   = mkSystemVarNameEncoded new_uniq FSLIT("lit")
                -- The "encoded" bit means that we don't need to z-encode
                -- the string every time we call this!
        lit_inst = LitInst lit_nm lit expected_ty loc
@@ -571,7 +569,12 @@ addInst :: DynFlags -> InstEnv -> DFunId -> TcM InstEnv
 addInst dflags home_ie dfun
   = do {       -- Instantiate the dfun type so that we extend the instance
                -- envt with completely fresh template variables
-         (tvs', theta', tau') <- tcInstType (idType dfun)
+               -- This is important because the template variables must
+               -- not overlap with anything in the things being looked up
+               -- (since we do unification).  
+               -- We use tcSkolType because we don't want to allocate fresh
+               -- *meta* type variables.  
+         (tvs', theta', tau') <- tcSkolType (InstSkol dfun) (idType dfun)
        ; let   (cls, tys') = tcSplitDFunHead tau'
                dfun'       = setIdType dfun (mkSigmaTy tvs' theta' tau')           
 
@@ -704,8 +707,13 @@ lookupInst (Dict _ _ _) = returnM NoInstance
 instantiate_dfun :: TvSubst -> DFunId -> TcPredType -> InstLoc -> TcM LookupInstResult
 instantiate_dfun tenv dfun_id pred loc
   = -- tenv is a substitution that instantiates the dfun_id 
-    -- to match the requested result type.   However, the dfun
-    -- might have some tyvars that only appear in arguments
+    -- to match the requested result type.   
+    -- 
+    -- We ASSUME that the dfun is quantified over the very same tyvars 
+    -- that are bound by the tenv.
+    -- 
+    -- However, the dfun
+    -- might have some tyvars that *only* appear in arguments
     -- dfun :: forall a b. C a b, Ord b => D [a]
     -- We instantiate b to a flexi type variable -- it'll presumably
     -- become fixed later via functional dependencies
@@ -731,7 +739,7 @@ instantiate_dfun tenv dfun_id pred loc
     mappM tcInstTyVar open_tvs `thenM` \ open_tvs' ->
     let
        tenv' = extendTvSubstList tenv open_tvs (mkTyVarTys open_tvs')
-               -- Since the tyvars are freshly made, they cannot possibly be captured by
+               -- Since the open_tvs' are freshly made, they cannot possibly be captured by
                -- any nested for-alls in rho.  So the in-scope set is unchanged
        dfun_rho   = substTy tenv' rho
        (theta, _) = tcSplitPhiTy dfun_rho