Added error when using terminal weights in dynamic earley (Discussed in #324)

lark/load_grammar.py

@@ -796,7 +796,7 @@ class GrammarLoader:
 
             name = '__IGNORE_%d'% len(ignore_names)
             ignore_names.append(name)
-            term_defs.append((name, (t, 0)))
+            term_defs.append((name, (t, 1)))
 
         # Verify correctness 2
         terminal_names = set()

lark/parser_frontends.py

@@ -93,6 +93,8 @@ class XEarley:
     def _prepare_match(self, lexer_conf):
         self.regexps = {}
         for t in lexer_conf.tokens:
+            if t.priority != 1:
+                raise ValueError("Dynamic Earley doesn't support weights on terminals", t, t.priority)
             regexp = t.pattern.to_regexp()
             try:
                 width = get_regexp_width(regexp)[0]