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  /*
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   Copyright (c) 2005-2009 Terence Parr
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 package org.antlr.runtime.tree;
 
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. Override if you want another kind of node to be built.
 
 	public Object create(Token payload);

Duplicate a single tree node. Override if you want another kind of node to be built.
 
 	public Object dupNode(Object treeNode);

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

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();

Return a tree node representing an error. This node records the tokens consumed during error recovery. The start token indicates the input symbol at which the error was detected. The stop token indicates the last symbol consumed during recovery. You must specify the input stream so that the erroneous text can be packaged up in the error node. The exception could be useful to some applications; default implementation stores ptr to it in the CommonErrorNode. This only makes sense during token parsing, not tree parsing. Tree parsing should happen only when parsing and tree construction succeed.
 
 	public Object errorNode(TokenStream inputToken startToken stopRecognitionException e);

Is tree considered a nil node used to make lists of child nodes?
 
 	public boolean isNil(Object tree);

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 you can decide it is ok to move children to t via t.children = child.children; i.e., without copying the array. Just make sure that this is consistent with have the user will build ASTs. Do nothing if t or child is null.
 
 	public void addChild(Object tObject 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 newRootObject 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().
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 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 newRootObject 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 tokenTypeToken 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 tokenTypeToken fromTokenString 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 tokenTypeString 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 tint type);
	public String getText(Object t);

Node constructors can set the text of a node
	public void setText(Object tString text);

Return the token object from which this node was created. Currently used only for printing an error message. The error display routine in BaseRecognizer needs to display where the input the error occurred. If your tree of limitation does not store information that can lead you to the token, you can create a token filled with the appropriate information and pass that back. See BaseRecognizer.getErrorMessage().
	public Token getToken(Object t);

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 tToken startTokenToken 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 tint i);

Set ith child (0..n-1) to t; t must be non-null and non-nil node
	public void setChild(Object tint iObject child);

Remove ith child and shift children down from right.
	public Object deleteChild(Object tint i);

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

Who is the parent node of this node; if null, implies node is root. If your node type doesn't handle this, it's ok but the tree rewrites in tree parsers need this functionality.
	public Object getParent(Object t);
	public void setParent(Object tObject parent);

What index is this node in the child list? Range: 0..n-1 If your node type doesn't handle this, it's ok but the tree rewrites in tree parsers need this functionality.
	public int getChildIndex(Object t);
	public void setChildIndex(Object tint index);

Replace from start to stop child index of parent with t, which might be a list. Number of children may be different after this call. If parent is null, don't do anything; must be at root of overall tree. Can't replace whatever points to the parent externally. Do nothing.
	public void replaceChildren(Object parentint startChildIndexint stopChildIndexObject t);
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