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java.lang.Objectpolyglot.visit.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)
|
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)
|
Node |
override(Node 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)
|
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
.
n
- The root of the subtree to be traversed.
null
if it
is to continue.public Node override(Node n)
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
.
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)
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.
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)
public NodeVisitor begin()
null
is returned, the ast is not traversed.
public void finish()
public void finish(Node ast)
public java.lang.String toString()
public Node visitEdge(Node parent, Node child)
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