Major refactoring of the type inference engine

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

diff --git a/compiler/typecheck/TcExpr.lhs b/compiler/typecheck/TcExpr.lhs
index 297b4e8..3f5a258 100644 (file)
--- a/compiler/typecheck/TcExpr.lhs
+++ b/compiler/typecheck/TcExpr.lhs
@@ -82,7 +82,7 @@ tcPolyExpr expr res_ty
 
 tcPolyExprNC expr res_ty
   = do { traceTc "tcPolyExprNC" (ppr res_ty)
-       ; (gen_fn, expr') <- tcGen (GenSkol res_ty) res_ty $ \ _ rho ->
+       ; (gen_fn, expr') <- tcGen GenSigCtxt res_ty $ \ _ rho ->
                            tcMonoExprNC expr rho
        ; return (mkLHsWrap gen_fn expr') }
 
@@ -191,7 +191,7 @@ tcExpr (ExprWithTySig expr sig_ty) res_ty
 
       -- Remember to extend the lexical type-variable environment
       ; (gen_fn, expr') 
-            <- tcGen (SigSkol ExprSigCtxt) sig_tc_ty $ \ skol_tvs res_ty ->
+            <- tcGen ExprSigCtxt sig_tc_ty $ \ skol_tvs res_ty ->
               tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
                                -- See Note [More instantiated than scoped] in TcBinds
               tcMonoExprNC expr res_ty
@@ -819,7 +819,8 @@ tcApp fun args res_ty
        -- Typecheck the result, thereby propagating 
         -- info (if any) from result into the argument types
         -- Both actual_res_ty and res_ty are deeply skolemised
-        ; co_res <- unifyType actual_res_ty res_ty
+        ; co_res <- addErrCtxt (funResCtxt fun) $
+                    unifyType actual_res_ty res_ty
 
        -- Typecheck the arguments
        ; args1 <- tcArgs fun args expected_arg_tys
@@ -1384,6 +1385,10 @@ funAppCtxt fun arg arg_no
                    quotes (ppr fun) <> text ", namely"])
        2 (quotes (ppr arg))
 
+funResCtxt :: LHsExpr Name -> SDoc
+funResCtxt fun
+  = ptext (sLit "In the return type of a call of") <+> quotes (ppr fun)
+
 badFieldTypes :: [(Name,TcType)] -> SDoc
 badFieldTypes prs
   = hang (ptext (sLit "Record update for insufficiently polymorphic field")