X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcExpr.lhs;h=39e8a5c959a0689a9db7fa1214ca92e9aa85a9ca;hb=970d5b88b1554bbdd7e459dae41aab3668ae897a;hp=c3bc64bbc31a60578bbcb58ae3f82ddf6b884da6;hpb=a1d112a19d73389723351789392fd5fd5951e0c4;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcExpr.lhs b/compiler/typecheck/TcExpr.lhs
index c3bc64b..39e8a5c 100644
--- a/compiler/typecheck/TcExpr.lhs
+++ b/compiler/typecheck/TcExpr.lhs
@@ -29,6 +29,7 @@ import TcHsType
 import TcPat
 import TcMType
 import TcType
+import TcIface	( checkWiredInTyCon )
 import Id
 import DataCon
 import Name
@@ -302,10 +303,11 @@ tcExpr (ExplicitTuple exprs boxity) res_ty
   = do	{ tvs <- newBoxyTyVars [argTypeKind | e <- exprs]
 	; let tup_tc     = tupleTyCon boxity (length exprs)
 	      tup_res_ty = mkTyConApp tup_tc (mkTyVarTys tvs)
-	; arg_tys   <- preSubType tvs (mkVarSet tvs) tup_res_ty res_ty
-	; exprs'    <-  tcPolyExprs exprs arg_tys
+	; checkWiredInTyCon tup_tc	-- Ensure instances are available
+	; arg_tys  <- preSubType tvs (mkVarSet tvs) tup_res_ty res_ty
+	; exprs'   <- tcPolyExprs exprs arg_tys
 	; arg_tys' <- mapM refineBox arg_tys
-	; co_fn <- tcFunResTy (tyConName tup_tc) (mkTyConApp tup_tc arg_tys') res_ty
+	; co_fn    <- tcFunResTy (tyConName tup_tc) (mkTyConApp tup_tc arg_tys') res_ty
 	; return (mkHsWrap co_fn (ExplicitTuple exprs' boxity)) }
 
 tcExpr (HsProc pat cmd) res_ty