X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcEnv.lhs;h=e1b9bd31b70c912cf74f7b61754aa43d89c77fb6;hp=cc50e50d732837f6d30763423dc6f151deb867e6;hb=84923cc7de2a93c22a2f72daf9ac863959efae13;hpb=f4510d27c5883fe7e8570f4dd49d45a8b0122f2c

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index cc50e50..e1b9bd3 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 +158,25 @@ 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)] -> 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 
+
+	   other -> famInstNotFound tycon tys other
+       }
 \end{code}
 
 %************************************************************************
@@ -656,4 +676,11 @@ 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 (ppr tycon <+> hsep (map pprParendType tys)))
+  where
+    msg = case what of
+		[] -> ptext SLIT("No instance for")
+		xs -> ptext SLIT("More than one instance for")
 \end{code}