cat-str: grammar in diagnostic.

* lib.c (cat_str_measure): add missing word "is" in
type error message.

1 files changed, 1 insertions, 1 deletions

diff --git a/lib.c b/lib.c
index 832d704b..1d06d645 100644
--- a/lib.c
+++ b/lib.c
@@ -6073,7 +6073,7 @@ static void cat_str_measure(struct cat_str *cs, val item, val self)
     return;
   }
 
-  uw_throwf(error_s, lit("~a: ~s neither character, string nor sequence"),
+  uw_throwf(error_s, lit("~a: ~s is neither a character, string nor sequence"),
             self, item, nao);
 oflow:
   uw_throwf(error_s, lit("~a: string length overflow"), self, nao);