public abstract class NodeVisitor extends java.lang.Object implements Copy<NodeVisitor>
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 separate 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| Modifier | Constructor and Description |
|---|---|
protected |
NodeVisitor()
Deprecated.
|
protected |
NodeVisitor(Lang lang) |
| Modifier and Type | Method and Description |
|---|---|
NodeVisitor |
begin()
The begin method is called before the entire tree is visited.
|
NodeVisitor |
copy() |
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) |
Lang |
lang() |
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() |
<N extends Node> |
visitEdge(Node parent,
N child)
Visit the edge between the parent node
parent, and child
node child. |
<N extends Node> |
visitEdgeNoOverride(Node parent,
N child)
Visit the edge between the parent node
parent, and child
node child, without invoking override for
the child. |
@Deprecated protected NodeVisitor()
protected NodeVisitor(Lang lang)
public Lang lang()
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 overridden, enter and
leave are each called exactly once.
Note that if old == n then the visitor 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 overridden, enter and
leave are each called exactly once.
Note that if old == n then the visitor 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.Objectpublic <N extends Node> N visitEdge(Node parent, N 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
Node.visit(NodeVisitor) instead
of polyglot.ast.Node.visitChild(Node, NodeVisitor).child - the child node of parent to be visited.child after the
subtree rooted at child has been recursively visited.public <N extends Node> N visitEdgeNoOverride(Node parent, N child)
parent, and child
node child, without invoking override for
the child. This method recursively visits the subtree rooted at
child.parent - child - child after the
subtree rooted at child has been recursively visited.public NodeVisitor copy()
copy in interface Copy<NodeVisitor>