1 /* 2 * [The "BSD licence"] 3 * Copyright (c) 2005-2008 Terence Parr 4 * All rights reserved. 5 * 6 * Conversion to C#: 7 * Copyright (c) 2008-2009 Sam Harwell, Pixel Mine, Inc. 8 * All rights reserved. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. The name of the author may not be used to endorse or promote products 19 * derived from this software without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 22 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 23 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 24 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 25 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 26 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 28 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 29 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 30 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31 */ 32 33 namespace Antlr.Runtime.Tree 34 { Func(T arg)35 public delegate TResult Func<T, TResult>(T arg); Action()36 public delegate void Action(); 37 38 /** 39 Cut-n-paste from material I'm not using in the book anymore (edit later 40 to make sense): 41 42 Now, how are we going to test these tree patterns against every 43 subtree in our original tree? In what order should we visit nodes? 44 For this application, it turns out we need a simple ``apply once'' 45 rule application strategy and a ``down then up'' tree traversal 46 strategy. Let's look at rule application first. 47 48 As we visit each node, we need to see if any of our patterns match. If 49 a pattern matches, we execute the associated tree rewrite and move on 50 to the next node. In other words, we only look for a single rule 51 application opportunity (we'll see below that we sometimes need to 52 repeatedly apply rules). The following method applies a rule in a @cl 53 TreeParser (derived from a tree grammar) to a tree: 54 55 here is where weReferenced code/walking/patterns/TreePatternMatcher.java 56 57 It uses reflection to lookup the appropriate rule within the generated 58 tree parser class (@cl Simplify in this case). Most of the time, the 59 rule will not match the tree. To avoid issuing syntax errors and 60 attempting error recovery, it bumps up the backtracking level. Upon 61 failure, the invoked rule immediately returns. If you don't plan on 62 using this technique in your own ANTLR-based application, don't sweat 63 the details. This method boils down to ``call a rule to match a tree, 64 executing any embedded actions and rewrite rules.'' 65 66 At this point, we know how to define tree grammar rules and how to 67 apply them to a particular subtree. The final piece of the tree 68 pattern matcher is the actual tree traversal. We have to get the 69 correct node visitation order. In particular, we need to perform the 70 scalar-vector multiply transformation on the way down (preorder) and 71 we need to reduce multiply-by-zero subtrees on the way up (postorder). 72 73 To implement a top-down visitor, we do a depth first walk of the tree, 74 executing an action in the preorder position. To get a bottom-up 75 visitor, we execute an action in the postorder position. ANTLR 76 provides a standard @cl TreeVisitor class with a depth first search @v 77 visit method. That method executes either a @m pre or @m post method 78 or both. In our case, we need to call @m applyOnce in both. On the way 79 down, we'll look for @r vmult patterns. On the way up, 80 we'll look for @r mult0 patterns. 81 */ 82 public class TreeFilter : TreeParser 83 { 84 protected ITokenStream originalTokenStream; 85 protected ITreeAdaptor originalAdaptor; 86 TreeFilter( ITreeNodeStream input )87 public TreeFilter( ITreeNodeStream input ) 88 : this( input, new RecognizerSharedState() ) 89 { 90 } TreeFilter( ITreeNodeStream input, RecognizerSharedState state )91 public TreeFilter( ITreeNodeStream input, RecognizerSharedState state ) 92 : base( input, state ) 93 { 94 originalAdaptor = input.TreeAdaptor; 95 originalTokenStream = input.TokenStream; 96 } 97 ApplyOnce( object t, Action whichRule )98 public virtual void ApplyOnce( object t, Action whichRule ) 99 { 100 if ( t == null ) 101 return; 102 103 try 104 { 105 // share TreeParser object but not parsing-related state 106 state = new RecognizerSharedState(); 107 input = new CommonTreeNodeStream( originalAdaptor, t ); 108 ( (CommonTreeNodeStream)input ).TokenStream = originalTokenStream; 109 BacktrackingLevel = 1; 110 whichRule(); 111 BacktrackingLevel = 0; 112 } 113 catch ( RecognitionException ) 114 { 115 } 116 } 117 Downup( object t )118 public virtual void Downup( object t ) 119 { 120 TreeVisitor v = new TreeVisitor( new CommonTreeAdaptor() ); 121 Func<object, object> pre = delegate(object o) 122 { 123 ApplyOnce( o, Topdown ); 124 return o; 125 }; 126 Func<object, object> post = delegate(object o) 127 { 128 ApplyOnce( o, Bottomup ); 129 return o; 130 }; 131 v.Visit( t, pre, post ); 132 } 133 134 // methods the downup strategy uses to do the up and down rules. 135 // to override, just define tree grammar rule topdown and turn on 136 // filter=true. Topdown()137 protected virtual void Topdown() 138 { 139 } Bottomup()140 protected virtual void Bottomup() 141 { 142 } 143 } 144 } 145