"," now elicits a warning, rather than being

a token; this is more compatible with byacc.

src/scan-gram.l

@@ -266,11 +266,15 @@ splice	 (\\[ \f\t\v]*\n)*
   "="                     return EQUAL;
   ":"                     rule_length = 0; return COLON;
   "|"                     rule_length = 0; return PIPE;
-  ","                     return COMMA;
   ";"                     return SEMICOLON;
 
   [ \f\n\t\v]  STEP;
 
+  "," {
+    warn_at (*loc, _("stray `,' treated as white space"));
+    STEP;
+  }
+
   {id}        {
     val->symbol = symbol_get (yytext, *loc);
     rule_length++;