From d44658fa3f6d15f5d9ef4e21966373d3700e39b0 Mon Sep 17 00:00:00 2001
From: Erez Shinan <erezshin+git@gmail.com>
Date: Sun, 5 Feb 2017 17:46:32 +0200
Subject: [PATCH] Now supports empty rules. Added some tests. All tests
 passing.

---
 lark/grammar_analysis.py |  8 ++++----
 lark/lark.py             |  3 ++-
 lark/load_grammar.py     |  8 +++++++-
 lark/parser.py           |  7 +++++--
 lark/tree.py             | 11 +++++++++--
 5 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/lark/grammar_analysis.py b/lark/grammar_analysis.py
index cc051ca..fb1ddb8 100644
--- a/lark/grammar_analysis.py
+++ b/lark/grammar_analysis.py
@@ -15,7 +15,6 @@ class Rule(object):
         expansion : a list of symbols
     """
     def __init__(self, origin, expansion, alias=None):
-        assert expansion, "No support for empty rules"
         self.origin = origin
         self.expansion = expansion
         self.alias = alias
@@ -91,9 +90,10 @@ class GrammarAnalyzer(object):
                 init_ptr = RulePtr(r, 0)
                 init_ptrs.add(init_ptr)
 
-                new_r = init_ptr.next
-                if not is_terminal(new_r):
-                    yield new_r
+                if r.expansion: # if not empty rule
+                    new_r = init_ptr.next
+                    if not is_terminal(new_r):
+                        yield new_r
 
         _ = list(bfs([rule], _expand_rule))
 
diff --git a/lark/lark.py b/lark/lark.py
index 87d19bd..19996fa 100644
--- a/lark/lark.py
+++ b/lark/lark.py
@@ -32,7 +32,6 @@ class LarkOptions(object):
         self.debug = bool(o.pop('debug', False))
         self.only_lex = bool(o.pop('only_lex', False))
         self.keep_all_tokens = bool(o.pop('keep_all_tokens', False))
-        self.keep_empty_trees = bool(o.pop('keep_empty_trees', True))
         self.tree_class = o.pop('tree_class', Tree)
         self.cache_grammar = o.pop('cache_grammar', False)
         self.ignore_postproc = bool(o.pop('ignore_postproc', False))
@@ -42,6 +41,8 @@ class LarkOptions(object):
         assert self.parser in ENGINE_DICT
         if self.parser == 'earley' and self.transformer:
             raise ValueError('Cannot specify an auto-transformer when using the Earley algorithm. Please use your transformer on the resulting parse tree, or use a different algorithm (i.e. lalr)')
+        if self.keep_all_tokens:
+            raise NotImplementedError("Not implemented yet!")
 
         if o:
             raise ValueError("Unknown options: %s" % o.keys())
diff --git a/lark/load_grammar.py b/lark/load_grammar.py
index 01a4aa5..5b4e037 100644
--- a/lark/load_grammar.py
+++ b/lark/load_grammar.py
@@ -74,7 +74,7 @@ RULES = [
     ('expansion', ['_expansion']),
     ('expansion', ['_expansion', 'TO', 'RULE']),
 
-    ('_expansion', ['expr']),
+    ('_expansion', []),
     ('_expansion', ['_expansion', 'expr']),
 
     ('expr', ['atom']),
@@ -149,6 +149,12 @@ class SaveDefinitions(object):
 
     def tokenvalue(self, tokenvalue):
         value = tokenvalue.value[1:-1]
+        import codecs
+        decoder = codecs.getdecoder('unicode_escape')
+        if '\u' in value:
+            # XXX for now, you can't mix unicode escaping and unicode characters at the same token
+            value = decoder(value)[0]
+
         if tokenvalue.type == 'STRING':
             value = re.escape(value)
         return tokenvalue, value
diff --git a/lark/parser.py b/lark/parser.py
index 2695009..5d66164 100644
--- a/lark/parser.py
+++ b/lark/parser.py
@@ -26,8 +26,11 @@ class Parser(object):
                 raise ParseError("Unexpected input %r.\nExpected: %s\nContext: %s" % (key, expected, context))
 
         def reduce(rule):
-            s = stack[-len(rule.expansion):]
-            del stack[-len(rule.expansion):]
+            if rule.expansion:
+                s = stack[-len(rule.expansion):]
+                del stack[-len(rule.expansion):]
+            else:
+                s = []
 
             res = self.callbacks[rule]([x[0] for x in s])
 
diff --git a/lark/tree.py b/lark/tree.py
index a056430..5f91605 100644
--- a/lark/tree.py
+++ b/lark/tree.py
@@ -1,3 +1,4 @@
+from copy import deepcopy
 from utils import inline_args
 
 class Tree(object):
@@ -29,6 +30,8 @@ class Tree(object):
             kid = self.children[i]
             self.children[i:i+1] = kid.children
 
+    def __eq__(self, other):
+        return self.data == other.data and self.children == other.children
 
     # def find_path(self, pred):
     #     if pred(self):
@@ -49,8 +52,12 @@ class Tree(object):
     #     x = self.follow_path(path[:-1])
     #     x.children[path[-1]] = value
 
-    def clone(self):
-        return Tree(self.data, [c.clone() if isinstance(c, Tree) else c for c in self.children])
+    # def clone(self):
+    #     return Tree(self.data, [c.clone() if isinstance(c, Tree) else c for c in self.children])
+
+    def __deepcopy__(self, memo):
+        return type(self)(self.data, deepcopy(self.children, memo))
+
 
 
 class Transformer(object):