polyglot.visit
Class AscriptionVisitor

java.lang.Object
  polyglot.visit.NodeVisitor
      polyglot.visit.HaltingVisitor
          polyglot.visit.ErrorHandlingVisitor
              polyglot.visit.ContextVisitor
                  polyglot.visit.AscriptionVisitor

All Implemented Interfaces:

java.lang.Cloneable, Copy

Direct Known Subclasses:

PaoBoxer

public class AscriptionVisitor
extends ContextVisitor

Visitor which allows type information to be utilized to perform AST modifications. The major advantage of this visitor is the new ascribe() method, which allows AST translations based on the expression and also the type that is expected. For the base translation (standard Java), the type of the expression and the type that is expceted are the same. Language extensions however may not have this property, and can take advantage of the ascribe method to transform the AST into a different form that will pass Java type-checking.

See Also:

ascribe(polyglot.ast.Expr, polyglot.types.Type)

Field Summary

Fields inherited from class polyglot.visit.ContextVisitor

context

Fields inherited from class polyglot.visit.ErrorHandlingVisitor

error, job, nf, ts

Constructor Summary

AscriptionVisitor(Job job, TypeSystem ts, NodeFactory nf)
Default constructor.

Method Summary

Expr	ascribe(Expr e, Type toType) The ascribe() method is called for each expression and is passed the type the expression is used at rather than the type the type checker assigns to it.
NodeVisitor	enterCall(Node parent, Node n) Sets up the expected type information for later calls to ascribe().
Node	leaveCall(Node old, Node n, NodeVisitor v) Calls ascribe() with the expected type and expression as appropriate.
AscriptionVisitor	pop()
Type	toType() Returns the type that is expected of the expression that is being visited.

Methods inherited from class polyglot.visit.ContextVisitor

addDecls, begin, context, context, enter, enterScope, leave, superEnter

Methods inherited from class polyglot.visit.ErrorHandlingVisitor

catchErrors, enterCall, enterError, errorQueue, job, leaveCall, nodeFactory, typeSystem

Methods inherited from class polyglot.visit.HaltingVisitor

bypass, bypass, bypassChildren, copy, override, visitChildren

Methods inherited from class polyglot.visit.NodeVisitor

enter, finish, finish, leave, override, toString, visitEdge

Methods inherited from class java.lang.Object

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

Constructor Detail

AscriptionVisitor

public AscriptionVisitor(Job job,
                         TypeSystem ts,
                         NodeFactory nf)

Default constructor. See the constructor in ErrorHandingVisitor for more details.

See Also:

ErrorHandlingVisitor.ErrorHandlingVisitor(polyglot.frontend.Job, polyglot.types.TypeSystem, polyglot.ast.NodeFactory)

Method Detail

pop

public AscriptionVisitor pop()

toType

public Type toType()

Returns the type that is expected of the expression that is being visited.

enterCall

public NodeVisitor enterCall(Node parent,
                             Node n)
                      throws SemanticException

Sets up the expected type information for later calls to ascribe(). Other than that, plays the same role as the enterCall method in ErrorHandlingVisitor.

Overrides:

enterCall in class ErrorHandlingVisitor

n - The root of the subtree to be traversed.

Returns:

The ErrorHandlingVisitor which should be used to visit the children of n.

Throws:

SemanticException

See Also:

NodeVisitor.enter(Node, Node)

ascribe

public Expr ascribe(Expr e,
                    Type toType)
             throws SemanticException

The ascribe() method is called for each expression and is passed the type the expression is used at rather than the type the type checker assigns to it. For instance, with the following code: Object o = new Integer(3); ascribe() will be called with expression new Integer(3) and type Object.

Parameters:

e - The expression that is being visited

toType - The type that the parent node is expecting.

Returns:

The new translated Expr node, or if nothing has changed, just e.

Throws:

SemanticException

leaveCall

public Node leaveCall(Node old,
                      Node n,
                      NodeVisitor v)
               throws SemanticException

Calls ascribe() with the expected type and expression as appropriate. Otherwise functionally the same as the leaveCall method in ErrorHandlingVisitor.

Overrides:

leaveCall in class ErrorHandlingVisitor

Parameters:

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.

Returns:

The final result of the traversal of the tree rooted at n.

Throws:

SemanticException

See Also:

NodeVisitor.leave(Node, Node, NodeVisitor)