net.sf.saxon.query
Class UnboundFunctionLibrary

java.lang.Object
  net.sf.saxon.query.UnboundFunctionLibrary

All Implemented Interfaces:

Serializable, FunctionLibrary

public class UnboundFunctionLibrary
extends Object
implements FunctionLibrary

An UnboundFunctionLibrary is not a real function library; rather, it is used to keep track of function calls that cannot yet be bound to a known declared function, but will have to be bound when all user-declared functions are available.

See Also:

Serialized Form

Constructor Summary

UnboundFunctionLibrary()
Create an XQueryFunctionLibrary

Method Summary

Expression	bind(StructuredQName functionName, Expression[] arguments, StaticContext env) Identify a (namespace-prefixed) function appearing in the expression.
void	bindUnboundFunctionCalls(XQueryFunctionBinder lib, Configuration config) Bind function calls that could not be bound when first encountered.
FunctionLibrary	copy() This method creates a copy of a FunctionLibrary: if the original FunctionLibrary allows new functions to be added, then additions to this copy will not affect the original, or vice versa.
boolean	isAvailable(StructuredQName functionName, int arity) Test whether a function with a given name and arity is available.

Methods inherited from class java.lang.Object

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

Constructor Detail

UnboundFunctionLibrary

public UnboundFunctionLibrary()

Create an XQueryFunctionLibrary

Method Detail

isAvailable

public boolean isAvailable(StructuredQName functionName,
                           int arity)

Test whether a function with a given name and arity is available. This supports the function-available() function in XSLT. Since this library is used only in XQuery, and contains no real functions, we always return false

Specified by:

isAvailable in interface FunctionLibrary

Parameters:

functionName - the name of the function required

arity - The number of arguments. This is set to -1 in the case of the single-argument function-available() function; in this case the method should return true if there is some

Returns:

true if a function of this name and arity is available for calling.

bind

public Expression bind(StructuredQName functionName,
                       Expression[] arguments,
                       StaticContext env)
                throws XPathException

Identify a (namespace-prefixed) function appearing in the expression. This method is called by the XQuery parser to resolve function calls found within the query.

Note that a function call may appear earlier in the query than the definition of the function to which it is bound. Unlike XSLT, we cannot search forwards to find the function definition. Binding of function calls is therefore a two-stage process; at the time the function call is parsed, we simply register it as pending; subsequently at the end of query parsing all the pending function calls are resolved. Another consequence of this is that we cannot tell at the time a function call is parsed whether it is a call to an internal (XSLT or XQuery) function or to an extension function written in Java.

Specified by:

bind in interface FunctionLibrary

Parameters:

functionName - the QName of the function being called

arguments - The expressions supplied statically in arguments to the function call. The length of this array represents the arity of the function. The intention is that the static type of the arguments (obtainable via getItemType() and getCardinality()) may be used as part of the binding algorithm. In some cases it may be possible for the function to be pre-evaluated at compile time, for example if these expressions are all constant values.

The conventions of the XPath language demand that the results of a function depend only on the values of the expressions supplied as arguments, and not on the form of those expressions. For example, the result of f(4) is expected to be the same as f(2+2). The actual expression is supplied here to enable the binding mechanism to select the most efficient possible implementation (including compile-time pre-evaluation where appropriate).

env - The static context of the function call

Returns:

an Expression representing the function call. This will normally be a FunctionCall, but it may be rewritten as some other expression.

Throws:

XPathException - if the function call is invalid, either because it is an unprefixed call to a non-system function, or because it is calling a system function that is available in XSLT only. A prefixed function call that cannot be recognized at this stage is assumed to be a forwards reference, and is bound later when bindUnboundFunctionCalls() is called.

bindUnboundFunctionCalls

public void bindUnboundFunctionCalls(XQueryFunctionBinder lib,
                                     Configuration config)
                              throws XPathException

Bind function calls that could not be bound when first encountered. These will either be forwards references to functions declared later in the query, or errors. This method is for internal use.

Parameters:

lib - A library containing all the XQuery functions that have been declared; the method searches this library for this missing function call

config - The Saxon configuration

Throws:

XPathException - if a function call refers to a function that has not been declared

copy

public FunctionLibrary copy()

This method creates a copy of a FunctionLibrary: if the original FunctionLibrary allows new functions to be added, then additions to this copy will not affect the original, or vice versa.

Specified by:

copy in interface FunctionLibrary

Returns:

a copy of this function library. This must be an instance of the original class.