net.sf.saxon.expr.parser

Class Evaluator

java.lang.Object

net.sf.saxon.expr.parser.Evaluator

public abstract class Evaluator
extends java.lang.Object

An Evaluator evaluates an expression to return a sequence

Field Summary

Fields

Modifier and Type	Field and Description
static Evaluator	EAGER_SEQUENCE An evaluator for arguments that in general return a sequence, where the sequence is evaluated eagerly.
static Evaluator	LAZY_SEQUENCE An evaluator for arguments that in general return a sequence, where the sequence is evaluated lazily on first use.
static Evaluator	LITERAL An evaluator for arguments supplied as a literal
static Evaluator	OPTIONAL_ITEM A (default) evaluator for arguments supplied as an expression that will return either a singleton item, or an empty sequence
static Evaluator	SINGLE_ITEM A (default) evaluator for arguments supplied as an expression that will always return a singleton item
static Evaluator	VARIABLE An evaluator for arguments supplied as a variable reference

Constructor Summary

Constructors

Constructor and Description
Evaluator()

Method Summary

Modifier and Type	Method and Description
abstract Sequence	evaluate(Expression expr, XPathContext context) Evaluate an expression to return a sequence

Methods inherited from class java.lang.Object

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

Field Detail

LITERAL

public static final Evaluator LITERAL

An evaluator for arguments supplied as a literal

VARIABLE

public static final Evaluator VARIABLE

An evaluator for arguments supplied as a variable reference

SINGLE_ITEM

public static final Evaluator SINGLE_ITEM

A (default) evaluator for arguments supplied as an expression that will always return a singleton item

OPTIONAL_ITEM

public static final Evaluator OPTIONAL_ITEM

A (default) evaluator for arguments supplied as an expression that will return either a singleton item, or an empty sequence

LAZY_SEQUENCE

public static final Evaluator LAZY_SEQUENCE

An evaluator for arguments that in general return a sequence, where the sequence is evaluated lazily on first use. This is appropriate when calling a function which might not use the value, or might not use all of it. It returns a LazySequence, which can only be read once, so this is only suitable for use when calling a function that can be trusted to read the argument once only.

EAGER_SEQUENCE

public static final Evaluator EAGER_SEQUENCE

An evaluator for arguments that in general return a sequence, where the sequence is evaluated eagerly. This is appropriate when it is known that the function will always use the entire value, or when it will use it more than once.

Constructor Detail

Evaluator

public Evaluator()

Method Detail

evaluate

public abstract Sequence evaluate(Expression expr,
                                  XPathContext context)
                           throws XPathException

Evaluate an expression to return a sequence

Parameters:

expr - the expression to be evaluated

context - the dynamic context for evaluation

Returns:

the result of the evaluation

Throws:

XPathException - if any dynamic error occurs during the evaluation