From: simonpj <unknown>
Date: Thu, 3 May 2001 09:04:43 +0000 (+0000)
Subject: [project @ 2001-05-03 09:04:43 by simonpj]
X-Git-Tag: Approximately_9120_patches~2015
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=0f7c4b885e64428f50e9fa943ecd42d3c5f39c35;p=ghc-hetmet.git

[project @ 2001-05-03 09:04:43 by simonpj]
Improve error message when two signature tyvars get unified
---

diff --git a/ghc/compiler/typecheck/TcMonoType.lhs b/ghc/compiler/typecheck/TcMonoType.lhs
index 0e622a0..9308390 100644
--- a/ghc/compiler/typecheck/TcMonoType.lhs
+++ b/ghc/compiler/typecheck/TcMonoType.lhs
@@ -821,15 +821,17 @@ checkSigTyVars sig_tyvars free_tyvars
 		-- acc maps a zonked type variable back to a signature type variable
 	  = case getTyVar_maybe ty of {
 	      Nothing ->			-- Error (a)!
-			returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (ppr ty) : msgs) ;
+			returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (quotes (ppr ty)) : msgs) ;
 
 	      Just tv ->
 
 	    case lookupVarEnv acc tv of {
 		Just sig_tyvar' -> 	-- Error (b) or (d)!
-			returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (ppr sig_tyvar') : msgs) ;
+			returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar thing : msgs)
+		    where
+			thing = ptext SLIT("another quantified type variable") <+> quotes (ppr sig_tyvar')
 
-		Nothing ->
+	      ; Nothing ->
 
 	    if tv `elemVarSet` globals	-- Error (c)! Type variable escapes
 					-- The least comprehensible, so put it last
@@ -913,7 +915,7 @@ escape_msg sig_tv tv globs frees
     vcat_first 0 (x:xs) = text "...others omitted..."
     vcat_first n (x:xs) = x $$ vcat_first (n-1) xs
 
-unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> quotes thing
+unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> thing
 mk_msg tv          = ptext SLIT("Quantified type variable") <+> quotes (ppr tv)
 \end{code}