xref: /external/antlr/antlr-3.4/runtime/CSharp2/Sources/Antlr3.Runtime/Antlr.Runtime.Tree/TreeFilter.cs

/*
 * [The "BSD licence"]
 * Copyright (c) 2005-2008 Terence Parr
 * All rights reserved.
 *
 * Conversion to C#:
 * Copyright (c) 2008-2009 Sam Harwell, Pixel Mine, Inc.
 * All rights reserved.
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 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
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 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
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 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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namespace Antlr.Runtime.Tree
{
    public delegate TResult Func<T, TResult>(T arg);
    public delegate void Action();

    /**
     Cut-n-paste from material I'm not using in the book anymore (edit later
     to make sense):

     Now, how are we going to test these tree patterns against every
    subtree in our original tree?  In what order should we visit nodes?
    For this application, it turns out we need a simple ``apply once''
    rule application strategy and a ``down then up'' tree traversal
    strategy.  Let's look at rule application first.

    As we visit each node, we need to see if any of our patterns match. If
    a pattern matches, we execute the associated tree rewrite and move on
    to the next node. In other words, we only look for a single rule
    application opportunity (we'll see below that we sometimes need to
    repeatedly apply rules). The following method applies a rule in a @cl
    TreeParser (derived from a tree grammar) to a tree:

    here is where weReferenced code/walking/patterns/TreePatternMatcher.java

    It uses reflection to lookup the appropriate rule within the generated
    tree parser class (@cl Simplify in this case). Most of the time, the
    rule will not match the tree.  To avoid issuing syntax errors and
    attempting error recovery, it bumps up the backtracking level.  Upon
    failure, the invoked rule immediately returns. If you don't plan on
    using this technique in your own ANTLR-based application, don't sweat
    the details. This method boils down to ``call a rule to match a tree,
    executing any embedded actions and rewrite rules.''

    At this point, we know how to define tree grammar rules and how to
    apply them to a particular subtree. The final piece of the tree
    pattern matcher is the actual tree traversal. We have to get the
    correct node visitation order.  In particular, we need to perform the
    scalar-vector multiply transformation on the way down (preorder) and
    we need to reduce multiply-by-zero subtrees on the way up (postorder).

    To implement a top-down visitor, we do a depth first walk of the tree,
    executing an action in the preorder position. To get a bottom-up
    visitor, we execute an action in the postorder position.  ANTLR
    provides a standard @cl TreeVisitor class with a depth first search @v
    visit method. That method executes either a @m pre or @m post method
    or both. In our case, we need to call @m applyOnce in both. On the way
    down, we'll look for @r vmult patterns. On the way up,
    we'll look for @r mult0 patterns.
     */
    public class TreeFilter : TreeParser
    {
        protected ITokenStream originalTokenStream;
        protected ITreeAdaptor originalAdaptor;

        public TreeFilter( ITreeNodeStream input )
            : this( input, new RecognizerSharedState() )
        {
        }
        public TreeFilter( ITreeNodeStream input, RecognizerSharedState state )
            : base( input, state )
        {
            originalAdaptor = input.TreeAdaptor;
            originalTokenStream = input.TokenStream;
        }

        public virtual void ApplyOnce( object t, Action whichRule )
        {
            if ( t == null )
                return;

            try
            {
                // share TreeParser object but not parsing-related state
                state = new RecognizerSharedState();
                input = new CommonTreeNodeStream( originalAdaptor, t );
                ( (CommonTreeNodeStream)input ).TokenStream = originalTokenStream;
                BacktrackingLevel = 1;
                whichRule();
                BacktrackingLevel = 0;
            }
            catch ( RecognitionException )
            {
            }
        }

        public virtual void Downup( object t )
        {
            TreeVisitor v = new TreeVisitor( new CommonTreeAdaptor() );
            Func<object, object> pre = delegate(object o)
            {
                ApplyOnce( o, Topdown );
                return o;
            };
            Func<object, object> post = delegate(object o)
            {
                ApplyOnce( o, Bottomup );
                return o;
            };
            v.Visit( t, pre, post );
        }

        // methods the downup strategy uses to do the up and down rules.
        // to override, just define tree grammar rule topdown and turn on
        // filter=true.
        protected virtual void Topdown()
        {
        }
        protected virtual void Bottomup()
        {
        }
    }
}