treeadaptor.java

ANTLR(ANother Tool for Language Recognition)它是这样的一种工具

/*
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 Copyright (c) 2005-2006 Terence Parr
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package org.antlr.runtime.tree;

import org.antlr.runtime.Token;

/** How to create and navigate trees.  Rather than have a separate factory
 *  and adaptor, I've merged them.  Makes sense to encapsulate.
 *
 *  This takes the place of the tree construction code generated in the
 *  generated code in 2.x and the ASTFactory.
 *
 *  I do not need to know the type of a tree at all so they are all
 *  generic Objects.  This may increase the amount of typecasting needed. :(
 */
public interface TreeAdaptor {
	// C o n s t r u c t i o n

	/** Create a tree node from Token object; for CommonTree type trees,
	 *  then the token just becomes the payload.  This is the most
	 *  common create call.
     */
	public Object create(Token payload);

	/** Duplicate tree recursively, using dupNode() for each node */
	public Object dupTree(Object tree);

	/** Duplicate a single tree node */
	public Object dupNode(Object treeNode);

	/** Return a nil node (an empty but non-null node) that can hold
	 *  a list of element as the children.  If you want a flat tree (a list)
	 *  use "t=adaptor.nil(); t.addChild(x); t.addChild(y);"
	 */
	public Object nil();

	/** Add a child to the tree t.  If child is a flat tree (a list), make all
	 *  in list children of t.  Warning: if t has no children, but child does
	 *  and child isNil then it is ok to move children to t via
	 *  t.children = child.children; i.e., without copying the array.  This
	 *  is for construction and I'm not sure it's completely general for
	 *  a tree's addChild method to work this way.  Make sure you differentiate
	 *  between your tree's addChild and this parser tree construction addChild
	 *  if it's not ok to move children to t with a simple assignment.
	 */
	public void addChild(Object t, Object child);

	/** If oldRoot is a nil root, just copy or move the children to newRoot.
	 *  If not a nil root, make oldRoot a child of newRoot.
	 *
	 *    old=^(nil a b c), new=r yields ^(r a b c)
	 *    old=^(a b c), new=r yields ^(r ^(a b c))
	 *
	 *  If newRoot is a nil-rooted single child tree, use the single
	 *  child as the new root node.
	 *
	 *    old=^(nil a b c), new=^(nil r) yields ^(r a b c)
	 *    old=^(a b c), new=^(nil r) yields ^(r ^(a b c))
	 *
	 *  If oldRoot was null, it's ok, just return newRoot (even if isNil).
	 *
	 *    old=null, new=r yields r
	 *    old=null, new=^(nil r) yields ^(nil r)
	 *
	 *  Return newRoot.  Throw an exception if newRoot is not a
	 *  simple node or nil root with a single child node--it must be a root
	 *  node.  If newRoot is ^(nil x) return x as newRoot.
	 *
	 *  Be advised that it's ok for newRoot to point at oldRoot's
	 *  children; i.e., you don't have to copy the list.  We are
	 *  constructing these nodes so we should have this control for
	 *  efficiency.
	 */
	public Object becomeRoot(Object newRoot, Object oldRoot);

	/** Given the root of the subtree created for this rule, post process
	 *  it to do any simplifications or whatever you want.  A required
	 *  behavior is to convert ^(nil singleSubtree) to singleSubtree
	 *  as the setting of start/stop indexes relies on a single non-nil root
	 *  for non-flat trees.
	 *
	 *  Flat trees such as for lists like "idlist : ID+ ;" are left alone
	 *  unless there is only one ID.  For a list, the start/stop indexes
	 *  are set in the nil node.
	 *
	 *  This method is executed after all rule tree construction and right
	 *  before setTokenBoundaries().
	 */
	public Object rulePostProcessing(Object root);

	/** For identifying trees.
	 *
	 *  How to identify nodes so we can say "add node to a prior node"?
	 *  Even becomeRoot is an issue.  Use System.identityHashCode(node)
	 *  usually.
	 */
	public int getUniqueID(Object node);


	// R e w r i t e  R u l e s

	/** Create a node for child and add as a child to root t.  Rather
	 *  than invoke create directly in the generated code for child,
	 *  the coder has more flexibility if the token itself is passed in.
	 *  You might want to do something different during rewrite construction
	 *  than you do during auto-AST construction (which has create() calls
	 *  generated in the output).
	 *
	 *  Be advised: when debugging ASTs, the DebugTreeAdaptor manually
	 *  calls create(Token child) and then plain addChild(node, node)
	 *  because it needs to trap calls to create, but it can't since it delegates
	 *  to not inherits from the TreeAdaptor.
	 */
	public void addChild(Object t, Token child);

	/** Create a node for newRoot make it the root of oldRoot.
	 *  If oldRoot is a nil root, just copy or move the children to newRoot.
	 *  If not a nil root, make oldRoot a child of newRoot.
	 *
	 *  Return node created for newRoot.
	 *
	 *  Be advised: when debugging ASTs, the DebugTreeAdaptor manually
	 *  calls create(Token child) and then plain becomeRoot(node, node)
	 *  because it needs to trap calls to create, but it can't since it delegates
	 *  to not inherits from the TreeAdaptor.
	 */
	public Object becomeRoot(Token newRoot, Object oldRoot);

	/** Create a new node derived from a token, with a new token type.
	 *  This is invoked from an imaginary node ref on right side of a
	 *  rewrite rule as IMAG[$tokenLabel].
	 *
	 *  This should invoke createToken(Token).
	 */
	public Object create(int tokenType, Token fromToken);

	/** Same as create(tokenType,fromToken) except set the text too.
	 *  This is invoked from an imaginary node ref on right side of a
	 *  rewrite rule as IMAG[$tokenLabel, "IMAG"].
	 *
	 *  This should invoke createToken(Token).
	 */
	public Object create(int tokenType, Token fromToken, String text);

	/** Create a new node derived from a token, with a new token type.
	 *  This is invoked from an imaginary node ref on right side of a
	 *  rewrite rule as IMAG["IMAG"].
	 *
	 *  This should invoke createToken(int,String).
	 */
	public Object create(int tokenType, String text);


	// C o n t e n t

	/** For tree parsing, I need to know the token type of a node */
	public int getType(Object t);

	/** Node constructors can set the type of a node */
	public void setType(Object t, int type);

	public String getText(Object t);

	/** Node constructors can set the text of a node */
	public void setText(Object t, String text);

	/** Where are the bounds in the input token stream for this node and
	 *  all children?  Each rule that creates AST nodes will call this
	 *  method right before returning.  Flat trees (i.e., lists) will
	 *  still usually have a nil root node just to hold the children list.
	 *  That node would contain the start/stop indexes then.
	 */
	public void setTokenBoundaries(Object t, Token startToken, Token stopToken);

	/** Get the token start index for this subtree; return -1 if no such index */
	public int getTokenStartIndex(Object t);

	/** Get the token stop index for this subtree; return -1 if no such index */
	public int getTokenStopIndex(Object t);


	// N a v i g a t i o n  /  T r e e  P a r s i n g

	/** Get a child 0..n-1 node */
	public Object getChild(Object t, int i);

	/** How many children?  If 0, then this is a leaf node */
	public int getChildCount(Object t);
}