From a5625a3be9f0280fe9674c3f14a36c5fc399929a Mon Sep 17 00:00:00 2001
From: Kevin Latimer <kevin@kevinlatimer.com>
Date: Mon, 18 Dec 2017 11:52:54 -0500
Subject: [PATCH 1/3] Add delete functionality

---
 lark/tree.py | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/lark/tree.py b/lark/tree.py
index 90583db..81a9929 100644
--- a/lark/tree.py
+++ b/lark/tree.py
@@ -95,7 +95,13 @@ class Transformer(object):
         return getattr(self, name)
 
     def transform(self, tree):
-        items = [self.transform(c) if isinstance(c, Tree) else c for c in tree.children]
+        items = []
+        for c in tree.children:
+            if isinstance(c, Tree):
+                try:
+                    items.append(self.transform(c))
+                except Erase:
+                    pass
         try:
             f = self._get_func(tree.data)
         except AttributeError:
@@ -110,6 +116,9 @@ class Transformer(object):
         return TransformerChain(self, other)
 
 
+class Erase(Exception):
+    pass
+
 class TransformerChain(object):
     def __init__(self, *transformers):
         self.transformers = transformers
@@ -166,7 +175,16 @@ class Transformer_NoRecurse(Transformer):
                 return f(t)
 
         for subtree in reversed(subtrees):
-            subtree.children = [_t(c) if isinstance(c, Tree) else c for c in subtree.children]
+            children = []
+            for c in subtree.children:
+                if isinstance(c, Tree):
+                    try:
+                        children.append(_t(c))
+                    except Erase:
+                        pass
+                else:
+                    children.append(c)
+            subtree.children = children
 
         return _t(tree)
 

From 26ce48b940aab5ea88a102407310d9fe77d25263 Mon Sep 17 00:00:00 2001
From: Kevin Latimer <kevin@kevinlatimer.com>
Date: Mon, 18 Dec 2017 14:51:07 -0500
Subject: [PATCH 2/3] Bug fix for Discard and make the syntax more pythonic

---
 lark/tree.py | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/lark/tree.py b/lark/tree.py
index 300e3f6..824bce6 100644
--- a/lark/tree.py
+++ b/lark/tree.py
@@ -106,11 +106,10 @@ class Transformer(object):
     def transform(self, tree):
         items = []
         for c in tree.children:
-            if isinstance(c, Tree):
-                try:
-                    items.append(self.transform(c))
-                except Discard:
-                    pass
+            try:
+                items.append(self.transform(c) if isinstance(c, Tree) else c)
+            except Discard:
+                pass
         try:
             f = self._get_func(tree.data)
         except AttributeError:
@@ -183,16 +182,13 @@ class Transformer_NoRecurse(Transformer):
             else:
                 return f(t)
 
-        for subtree in (subtrees):
+        for subtree in reversed(subtrees):
             children = []
             for c in subtree.children:
-                if isinstance(c, Tree):
-                    try:
-                        children.append(_t(c))
-                    except Discard:
-                        pass
-                else:
-                    children.append(c)
+                try:
+                    children.append(_t(c) if isinstance(c, Tree) else c)
+                except Discard:
+                    pass
             subtree.children = children
 
         return _t(tree)

From 240cf1ca2133ede2d95c791a482b32359b0bdfc4 Mon Sep 17 00:00:00 2001
From: Kevin Latimer <kevin@kevinlatimer.com>
Date: Mon, 18 Dec 2017 15:28:23 -0500
Subject: [PATCH 3/3] Bug fixes to Transformer_NoRecurse

---
 lark/tree.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lark/tree.py b/lark/tree.py
index 824bce6..f832857 100644
--- a/lark/tree.py
+++ b/lark/tree.py
@@ -182,7 +182,7 @@ class Transformer_NoRecurse(Transformer):
             else:
                 return f(t)
 
-        for subtree in reversed(subtrees):
+        for subtree in subtrees:
             children = []
             for c in subtree.children:
                 try: