package net.sf.saxon.expr;
import net.sf.saxon.Controller;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.value.Value;
import net.sf.saxon.event.SequenceOutputter;
import net.sf.saxon.event.PipelineConfiguration;
import net.sf.saxon.om.*;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.Type;
import net.sf.saxon.type.TypeHierarchy;
import java.util.Arrays;
import java.util.Iterator;
/**
* An abstract implementation of Expression designed to make it easy to implement new expressions,
* in particular, expressions to support extension instructions.
*/
public abstract class SimpleExpression extends Expression {
public static final Expression[] NO_ARGUMENTS = new Expression[0];
protected Expression[] arguments = NO_ARGUMENTS;
/**
* Constructor
*/
public SimpleExpression() {
}
/**
* Set the immediate sub-expressions of this expression.
* @param sub an array containing the sub-expressions of this expression
*/
public void setArguments(Expression[] sub) {
arguments = sub;
for (int i=0; i<sub.length; i++) {
adoptChildExpression(sub[i]);
}
}
/**
* Get the immediate sub-expressions of this expression.
* @return an array containing the sub-expressions of this expression
*/
public Iterator<Expression> iterateSubExpressions() {
return Arrays.asList(arguments).iterator();
}
/**
* Replace one subexpression by a replacement subexpression
* @param original the original subexpression
* @param replacement the replacement subexpression
* @return true if the original subexpression is found
*/
public boolean replaceSubExpression(Expression original, Expression replacement) {
boolean found = false;
for (int i=0; i<arguments.length; i++) {
if (arguments[i] == original) {
arguments[i] = replacement;
found = true;
}
}
return found;
}
/**
* Simplify the expression
* @return the simplified expression
* @param visitor an expression visitor
*/
public Expression simplify(ExpressionVisitor visitor) throws XPathException {
for (int i = 0; i < arguments.length; i++) {
if (arguments[i] != null) {
arguments[i] = visitor.simplify(arguments[i]);
}
}
return this;
}
public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
for (int i = 0; i < arguments.length; i++) {
if (arguments[i] != null) {
arguments[i] = visitor.typeCheck(arguments[i], contextItemType);
}
}
return this;
}
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
for (int i = 0; i < arguments.length; i++) {
if (arguments[i] != null) {
arguments[i] = visitor.optimize(arguments[i], contextItemType);
}
}
return this;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
*/
public Expression copy() {
throw new UnsupportedOperationException("copy");
}
/**
* Offer promotion for this subexpression. The offer will be accepted if the subexpression
* is not dependent on the factors (e.g. the context item) identified in the PromotionOffer.
* By default the offer is not accepted - this is appropriate in the case of simple expressions
* such as constant values and variable references where promotion would give no performance
* advantage. This method is always called at compile time.
*
* @param offer details of the offer, for example the offer to move
* expressions that don't depend on the context to an outer level in
* the containing expression
* @param parent
* @exception XPathException if any error is detected
* @return if the offer is not accepted, return this expression unchanged.
* Otherwise return the result of rewriting the expression to promote
* this subexpression
*/
public Expression promote(PromotionOffer offer, Expression parent) throws XPathException {
for (int i = 0; i < arguments.length; i++) {
if (arguments[i] != null) {
arguments[i] = doPromotion(this, arguments[i], offer);
}
}
return this;
}
/**
* Determine the data type of the items returned by this expression. This implementation
* returns "item()", which can be overridden in a subclass.
* @return the data type
* @param th the type hierarchy cache
*/
public ItemType getItemType(TypeHierarchy th) {
return Type.ITEM_TYPE;
}
/**
* Determine the static cardinality of the expression. This implementation
* returns "zero or more", which can be overridden in a subclass.
*/
public int computeCardinality() {
if ((getImplementationMethod() & Expression.EVALUATE_METHOD) == 0) {
return StaticProperty.ALLOWS_ONE_OR_MORE;
} else {
return StaticProperty.ALLOWS_ZERO_OR_ONE;
}
}
/**
* Compute the dependencies of an expression, as the union of the
* dependencies of its subexpressions. (This is overridden for path expressions
* and filter expressions, where the dependencies of a subexpression are not all
* propogated). This method should be called only once, to compute the dependencies;
* after that, getDependencies should be used.
* @return the depencies, as a bit-mask
*/
public int computeDependencies() {
return super.computeDependencies();
}
/**
* Evaluate an expression as a single item. This always returns either a single Item or
* null (denoting the empty sequence). No conversion is done. This method should not be
* used unless the static type of the expression is a subtype of "item" or "item?": that is,
* it should not be called if the expression may return a sequence. There is no guarantee that
* this condition will be detected.
*
* @param context The context in which the expression is to be evaluated
* @exception XPathException if any dynamic error occurs evaluating the
* expression
* @return the node or atomic value that results from evaluating the
* expression; or null to indicate that the result is an empty
* sequence
*/
public Item evaluateItem(XPathContext context) throws XPathException {
int m = getImplementationMethod();
if ((m & Expression.EVALUATE_METHOD) != 0) {
// this indicates an error in the user-written extension code
throw new AssertionError("evaluateItem() is not implemented in the subclass " + this.getClass());
} else if ((m & Expression.ITERATE_METHOD) != 0) {
return iterate(context).next();
} else {
Controller controller = context.getController();
XPathContext c2 = context.newMinorContext();
c2.setOrigin(this);
SequenceOutputter seq = controller.allocateSequenceOutputter(1);
PipelineConfiguration pipe = controller.makePipelineConfiguration();
pipe.setHostLanguage(getContainer().getHostLanguage());
seq.setPipelineConfiguration(pipe);
c2.setTemporaryReceiver(seq);
process(c2);
Item item = seq.getFirstItem();
seq.reset();
return item;
}
}
/**
* Return an Iterator to iterate over the values of a sequence. The value of every
* expression can be regarded as a sequence, so this method is supported for all
* expressions. This default implementation handles iteration for expressions that
* return singleton values: for non-singleton expressions, the subclass must
* provide its own implementation.
*
* @exception XPathException if any dynamic error occurs evaluating the
* expression
* @param context supplies the context for evaluation
* @return a SequenceIterator that can be used to iterate over the result
* of the expression
*/
public SequenceIterator iterate(XPathContext context) throws XPathException {
int m = getImplementationMethod();
if ((m & Expression.EVALUATE_METHOD) != 0) {
Item item = evaluateItem(context);
if (item==null) {
return EmptyIterator.getInstance();
} else {
return SingletonIterator.makeIterator(item);
}
} else if ((m & Expression.ITERATE_METHOD) != 0) {
// this indicates an error in the user-written extension code
throw new AssertionError("iterate() is not implemented in the subclass " + this.getClass());
} else {
Controller controller = context.getController();
XPathContext c2 = context.newMinorContext();
c2.setOrigin(this);
SequenceOutputter seq = controller.allocateSequenceOutputter(10);
PipelineConfiguration pipe = controller.makePipelineConfiguration();
pipe.setHostLanguage(getContainer().getHostLanguage());
seq.setPipelineConfiguration(pipe);
c2.setTemporaryReceiver(seq);
process(c2);
SequenceIterator result = Value.getIterator(seq.getSequence());
seq.reset();
return result;
}
}
/**
* Process the instruction, without returning any tail calls
* @param context The dynamic context, giving access to the current node,
* the current variables, etc.
*/
public void process(XPathContext context) throws XPathException {
int m = getImplementationMethod();
if ((m & Expression.EVALUATE_METHOD) == 0) {
SequenceIterator iter = iterate(context);
while (true) {
Item it = iter.next();
if (it==null) break;
context.getReceiver().append(it, locationId, NodeInfo.ALL_NAMESPACES);
}
} else {
Item item = evaluateItem(context);
context.getReceiver().append(item, locationId, NodeInfo.ALL_NAMESPACES);
}
}
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied output destination.
*/
public void explain(ExpressionPresenter destination) {
destination.startElement("userExpression");
destination.emitAttribute("class", getExpressionType());
for (int i = 0; i < arguments.length; i++) {
arguments[i].explain(destination);
}
destination.endElement();
}
/**
* Return a distinguishing name for the expression, for use in diagnostics.
* By default the class name is used.
* @return a distinguishing name for the expression (defaults to the name of the implementation class)
*/
public String getExpressionType() {
return getClass().getName();
}
}
//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
// you may not use this file except in compliance with the License. You may obtain a copy of the
// License at http://www.mozilla.org/MPL/
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License.
//
// The Original Code is: all this file.
//
// The Initial Developer of the Original Code is Michael H. Kay.
//
// Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
//
// Contributor(s): none.
//