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java.lang.Object polyglot.visit.NodeVisitor
public abstract class NodeVisitor
The NodeVisitor
represents an implementation of the "Visitor"
style of tree traversal. There is a convention among polyglot visitors
which states that traversals will lazily reconstruct the tree. That
is, the AST is functionally "modified" by creating new nodes on each
traversal, but only when necessary only when nodes (or their children) are
actually changed. Up to three seperate calls into the visitor may be invoked
for each AST node. override
allows the visitor to redefine the
entire traversal for a particular subtree. enter
notifies the
visitor that traversal of a particular subtree has begun.
leave
informs the visitor that traversal is finishing a
particular subtree.
Node.visit(polyglot.visit.NodeVisitor)
,
Node
Constructor Summary  

NodeVisitor()

Method Summary  

NodeVisitor 
begin()
The begin method is called before the entire tree is visited. 
NodeVisitor 
enter(Node n)
Begin normal traversal of a subtree rooted at n . 
NodeVisitor 
enter(Node parent,
Node n)
Begin normal traversal of a subtree rooted at n . 
void 
finish()
The finish method is called after the entire tree has been visited. 
void 
finish(Node ast)

Node 
leave(Node parent,
Node old,
Node n,
NodeVisitor v)
This method is called after all of the children of n
have been visited. 
Node 
leave(Node old,
Node n,
NodeVisitor v)
This method is called after all of the children of n
have been visited. 
Node 
override(Node n)
Given a tree rooted at n , the visitor has the option of
overriding all traversal of the children of n . 
Node 
override(Node parent,
Node n)
Given a tree rooted at n , the visitor has the option of
overriding all traversal of the children of n . 
java.lang.String 
toString()

Node 
visitEdge(Node parent,
Node child)
Visit the edge between the parent node parent , and child
node child . 
Methods inherited from class java.lang.Object 

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait 
Constructor Detail 

public NodeVisitor()
Method Detail 

public Node override(Node parent, Node n)
n
, the visitor has the option of
overriding all traversal of the children of n
. If no
changes were made to n
and the visitor wishes to prevent
further traversal of the tree, then it should return n
. If
changes were made to the subtree, then the visitor should return a
copy of n
with appropriate changes. Finally, if the
visitor does not wish to override traversal of the subtree rooted at
n
, then it should return null
.
The default implementation of this method is to call
override(n)
, as most subclasses do not need to know
the parent of the node n
.
parent
 The parent of n
,
null
if n
has no parent.n
 The root of the subtree to be traversed.
null
if it
is to continue.public Node override(Node n)
n
, the visitor has the option of
overriding all traversal of the children of n
. If no
changes were made to n
and the visitor wishes to prevent
further traversal of the tree, then it should return n
. If
changes were made to the subtree, then the visitor should return a
copy of n
with appropriate changes. Finally, if the
visitor does not wish to override traversal of the subtree rooted at
n
, then it should return null
.
This method is typically called by the method
override(parent, n)
. If a subclass overrides the
method override(parent, n)
then this method
may not be called.
n
 The root of the subtree to be traversed.
null
if it
is to continue.public NodeVisitor enter(Node parent, Node n)
n
. This gives
the visitor the option of changing internal state or returning a new
visitor which will be used to visit the children of n
.
The default implementation of this method is to call
enter(n)
, as most subclasses do not need to know
the parent of the node n
.
parent
 The parent of n
, null
if n
has no parent.n
 The root of the subtree to be traversed.
NodeVisitor
which should be used to visit the
children of n
.public NodeVisitor enter(Node n)
n
. This gives
the visitor the option of changing internal state or returning a new
visitor which will be used to visit the children of n
.
This method is typically called by the method
enter(parent, n)
. If a subclass overrides the
method enter(parent, n)
then this method
may not be called.
n
 The root of the subtree to be traversed.
NodeVisitor
which should be used to visit the
children of n
.public Node leave(Node parent, Node old, Node n, NodeVisitor v)
n
have been visited. In this case, these children were visited by the
visitor v
. This is the last chance for the visitor to
modify the tree rooted at n
. This method will be called
exactly the same number of times as entry
is called.
That is, for each node that is not overriden, enter
and
leave
are each called exactly once.
Note that if old == n
then the vistior should make a copy
of n
before modifying it. It should then return the
modified copy.
The default implementation of this method is to call
leave(old, n, v)
,
as most subclasses do not need to know the parent of the
node n
.
parent
 The parent of old
,
null
if old
has no parent.old
 The original state of root of the current subtree.n
 The current state of the root of the current subtree.v
 The NodeVisitor
object used to visit the children.
n
.public Node leave(Node old, Node n, NodeVisitor v)
n
have been visited. In this case, these children were visited by the
visitor v
. This is the last chance for the visitor to
modify the tree rooted at n
. This method will be called
exactly the same number of times as entry
is called.
That is, for each node that is not overriden, enter
and
leave
are each called exactly once.
Note that if old == n
then the vistior should make a copy
of n
before modifying it. It should then return the
modified copy.
This method is typically called by the method
leave(parent, old, n v)
.
If a subclass overrides the method
leave(parent, old, n v)
then this method may not be called.
old
 The original state of root of the current subtree.n
 The current state of the root of the current subtree.v
 The NodeVisitor
object used to visit the children.
n
.public NodeVisitor begin()
null
is returned, the ast is not traversed.
NodeVisitor
to traverse the ast with. If
null
is returned, the ast is not traversed.public void finish()
public void finish(Node ast)
public java.lang.String toString()
toString
in class java.lang.Object
public Node visitEdge(Node parent, Node child)
parent
, and child
node child
. This method recursively visits the subtree rooted
at child
.
parent
 the parent node of child
, null
if
child
was visited by calling
polyglot.ast.Node.visit(NodeVisitor)
instead
of Node.visitChild(Node, NodeVisitor)
.child
 the child node of parent
to be visited.
child
after the
subtree rooted at child
has been recursively visited.


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