[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 (file)
--- 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}