From 686e796a62438e0a504a992cd172e21cbf7e7e3f Mon Sep 17 00:00:00 2001
From: Erez Shinan <erezshin+git@gmail.com>
Date: Sun, 28 May 2017 19:50:18 +0300
Subject: [PATCH] Small improvements to Earley

---
 examples/python3.g     | 9 +++++----
 lark/parsers/earley.py | 8 +++++++-
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/examples/python3.g b/examples/python3.g
index 279c268..a382d0b 100644
--- a/examples/python3.g
+++ b/examples/python3.g
@@ -116,11 +116,12 @@ AWAIT: "await"
           | atom_expr "." NAME               -> getattr
           | atom
 
-?atom: "(" [yield_expr|testlist_comp] ")"
-     | "[" [testlist_comp] "]"
-     | "{" [dictorsetmaker] "}"
+?atom: "(" [yield_expr|testlist_comp] ")" -> tuple
+     | "[" [testlist_comp] "]"  -> list
+     | "{" [dictorsetmaker] "}" -> dict
      | NAME -> var
-     | number | string+ | "..."
+     | number | string+
+     | "..." -> ellipsis
      | "None"    -> const_none
      | "True"    -> const_true
      | "False"   -> const_false
diff --git a/lark/parsers/earley.py b/lark/parsers/earley.py
index dfe13c7..6014fee 100644
--- a/lark/parsers/earley.py
+++ b/lark/parsers/earley.py
@@ -107,7 +107,7 @@ class Column:
                         new_tree.rule = old_tree.rule
                         old_tree.set('_ambig', [new_tree])
                     if item.tree.children[0] is old_tree:   # XXX a little hacky!
-                        raise ParseError("Infinite recursion in grammar!")
+                        raise ParseError("Infinite recursion in grammar! (Rule %s)" % item.rule)
                     old_tree.children.append(item.tree)
                 else:
                     self.completed[item] = item
@@ -228,6 +228,12 @@ def _compare_drv(tree1, tree2):
     if not (isinstance(tree1, Tree) and isinstance(tree2, Tree)):
         return compare(tree1, tree2)
 
+    try:
+        rule1, rule2 = tree1.rule, tree2.rule
+    except AttributeError:
+        # Probably trees that don't take part in this parse (better way to distinguish?)
+        return compare(tree1, tree2)
+
     c = _compare_rules(tree1.rule, tree2.rule)
     if c:
         return c