X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcEnv.lhs;h=ff49db6af6b04448f5a032cbb551f2d397b58b4a;hb=a9b1d323161e1f696e364050e6675db71fab64e8;hp=cc50e50d732837f6d30763423dc6f151deb867e6;hpb=f4510d27c5883fe7e8570f4dd49d45a8b0122f2c;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index cc50e50..ff49db6 100644
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -17,7 +17,7 @@ module TcEnv(
 	tcLookupLocatedGlobal,	tcLookupGlobal, 
 	tcLookupField, tcLookupTyCon, tcLookupClass, tcLookupDataCon,
 	tcLookupLocatedGlobalId, tcLookupLocatedTyCon,
-	tcLookupLocatedClass, 
+	tcLookupLocatedClass, tcLookupFamInst,
 	
 	-- Local environment
 	tcExtendKindEnv, tcExtendKindEnvTvs,
@@ -61,6 +61,7 @@ import VarSet
 import VarEnv
 import RdrName
 import InstEnv
+import FamInstEnv
 import DataCon
 import TyCon
 import Class
@@ -157,6 +158,33 @@ tcLookupLocatedClass = addLocM tcLookupClass
 
 tcLookupLocatedTyCon :: Located Name -> TcM TyCon
 tcLookupLocatedTyCon = addLocM tcLookupTyCon
+
+-- Look up the representation tycon of a family instance.
+-- Return the rep tycon and the corresponding rep args
+tcLookupFamInst :: TyCon -> [Type] -> TcM (TyCon, [Type])
+tcLookupFamInst tycon tys
+  | not (isOpenTyCon tycon)
+  = return (tycon, tys)
+  | otherwise
+  = do { env <- getGblEnv
+       ; eps <- getEps
+       ; let instEnv = (eps_fam_inst_env eps, tcg_fam_inst_env env)
+       ; case lookupFamInstEnv instEnv tycon tys of
+
+	   [(subst, fam_inst)] | variable_only_subst -> 
+	     return (rep_tc, substTyVars subst (tyConTyVars rep_tc))
+		where	-- NB: assumption is that (tyConTyVars rep_tc) is in 
+			--     the domain of the substitution
+		  rep_tc              = famInstTyCon fam_inst
+		  subst_domain        = varEnvElts . getTvSubstEnv $ subst
+		  tvs		      = map (Type.getTyVar "tcLookupFamInst") 
+					    subst_domain
+		  variable_only_subst = all Type.isTyVarTy subst_domain &&
+					sizeVarSet (mkVarSet tvs) == length tvs
+					-- renaming may have no repetitions
+
+	   other -> famInstNotFound tycon tys other
+       }
 \end{code}
 
 %************************************************************************
@@ -656,4 +684,11 @@ notFound name
 wrongThingErr expected thing name
   = failWithTc (pprTcTyThingCategory thing <+> quotes (ppr name) <+> 
 		ptext SLIT("used as a") <+> text expected)
+
+famInstNotFound tycon tys what
+  = failWithTc (msg <+> quotes (pprTypeApp (ppr tycon) tys))
+  where
+    msg = ptext $ if length what > 1 
+		  then SLIT("More than one family instance for")
+		  else SLIT("No family instance exactly matching")
 \end{code}