Straightened out implicit coercions for indexed types

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

diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs
index 3449766..e186b36 100644 (file)
--- a/compiler/typecheck/TcInstDcls.lhs
+++ b/compiler/typecheck/TcInstDcls.lhs
@@ -33,7 +33,7 @@ import Type           ( zipOpenTvSubst, substTheta, mkTyConApp, mkTyVarTy,
                           splitFunTys, TyThing(ATyCon), isTyVarTy, tcEqType,
                           substTys, emptyTvSubst, extendTvSubst )
 import Coercion         ( mkSymCoercion )
-import TyCon            ( TyCon, tyConName, newTyConCo, tyConTyVars,
+import TyCon            ( TyCon, tyConName, newTyConCo_maybe, tyConTyVars,
                          isTyConAssoc, tyConFamInst_maybe,
                          assocTyConArgPoss_maybe )
 import DataCon         ( classDataCon, dataConTyCon, dataConInstArgTys )
@@ -550,7 +550,7 @@ tcInstDecl2 (InstInfo { iSpec = ispec,
   where
        -- For newtype T a = MkT <ty>
        -- The returned coercion has kind :: C (T a):=:C <ty>
-    co_fn tvs cls_tycon cls_inst_tys | Just co_con <- newTyConCo tycon
+    co_fn tvs cls_tycon cls_inst_tys | Just co_con <- newTyConCo_maybe tycon
           = ExprCoFn (mkTyConApp cls_tycon (drop_tail 1 cls_inst_tys ++
                       [mkSymCoercion (mkTyConApp co_con (map mkTyVarTy tvs))]))
           | otherwise
@@ -833,8 +833,9 @@ atInstCtxt name = ptext SLIT("In the associated type instance for") <+>
                  quotes (ppr name)
 
 mustBeVarArgErr ty = 
-  sep [ ptext SLIT("Arguments that do not correspond to a class parameter")
-      , ptext SLIT("must be variables:") <+> ppr ty
+  sep [ ptext SLIT("Arguments that do not correspond to a class parameter") <+>
+        ptext SLIT("must be variables")
+      , ptext SLIT("Instead of a variable, found") <+> ppr ty
       ]
 
 wrongATArgErr ty instTy =