[project @ 2001-04-30 10:48:57 by simonpj]

Improve error message

diff --git a/ghc/compiler/typecheck/TcBinds.lhs b/ghc/compiler/typecheck/TcBinds.lhs
index 5bd9cae..a50bc50 100644 (file)
--- a/ghc/compiler/typecheck/TcBinds.lhs
+++ b/ghc/compiler/typecheck/TcBinds.lhs
@@ -473,8 +473,7 @@ generalise binder_names mbind tau_tvs lie_req sigs
 
     tysig_names = [name | (TySigInfo name _ _ _ _ _ _ _) <- sigs]
 
-    doc | null sigs = ptext SLIT("banding(s) for")        <+> pprBinders binder_names
-       | otherwise = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
+    doc = ptext SLIT("type signature(s) for") <+> pprBinders binder_names
 
 -----------------------
        -- CHECK THAT ALL THE SIGNATURE CONTEXTS ARE UNIFIABLE
@@ -827,5 +826,5 @@ restrictedBindCtxtErr binder_names
                ptext SLIT("that falls under the monomorphism restriction")])
 
 -- Used in error messages
-pprBinders bndrs = braces (pprWithCommas ppr bndrs)
+pprBinders bndrs = pprWithCommas ppr bndrs
 \end{code}

diff --git a/ghc/compiler/typecheck/TcInstDcls.lhs b/ghc/compiler/typecheck/TcInstDcls.lhs
index 1a38a13..95add91 100644 (file)
--- a/ghc/compiler/typecheck/TcInstDcls.lhs
+++ b/ghc/compiler/typecheck/TcInstDcls.lhs
@@ -729,7 +729,8 @@ check_tyvars dflags clas inst_taus
   | otherwise                                = [the_err]
   where
     the_err = instTypeErr clas inst_taus msg
-    msg     = ptext SLIT("There must be at least one non-type-variable in the instance head")
+    msg     =  ptext SLIT("There must be at least one non-type-variable in the instance head")
+           $$ ptext SLIT("Use -fallow-undecidable-instances to lift this restriction")
 
 check_fundeps dflags theta clas inst_taus
   | checkInstFDs theta clas inst_taus = []