com.saxonica.codegen
Class ExpressionCompiler

java.lang.Object
  com.saxonica.codegen.ExpressionCompiler

Direct Known Subclasses:

ChooseCompiler, ContextItemCompiler, ErrorCompiler, ErrorExpressionCompiler, LiteralCompiler, ParentNodeExpressionCompiler, PushExpressionCompiler, RootExpressionCompiler, SequenceExpressionCompiler, SingletonExpressionCompiler, ToBooleanCompiler, TraceCompiler

public abstract class ExpressionCompiler
extends java.lang.Object

This abstract class represents the compiler (that is, Java code generator) for a particular kind of expression on the expression tree. The expression compiler is called by the CompilerService working its way down the expression tree in a top down fashion: there is a one-to-one correspondence between the classes implementing the expression on the expression tree and the compiler object used to generate Java code fragments. Various methods are supplied to compile expressions; exactly one of them is called, depending on the context in which the expression appears.

Constructor Summary

ExpressionCompiler()

Method Summary

void	compileAsLoop(CompilerService compiler, Expression expr, LoopAction action) Compile an XPath expression in the form of a loop.
abstract void	compilePush(CompilerService compiler, Expression exp) Generate Java code to execute the expression in push mode, that is, code to write events to the current output Receiver
abstract java.lang.String	compileToCharSequence(CompilerService compiler, Expression expr) Generate Java code to evaluate the expression as a CharSequence
abstract java.lang.String	compileToEffectiveBooleanValue(CompilerService compiler, Expression expr, ReturnAction options) Generate Java code to evaluate the effective boolean value of the expression
abstract java.lang.String	compileToItem(CompilerService compiler, Expression exp) Generate Java code to evaluate the expression as an Item
abstract java.lang.String	compileToIterator(CompilerService compiler, Expression exp) Generate Java code to evaluate the expression as a SequenceIterator
java.lang.String	compileToValueRepresentation(CompilerService compiler, Expression expr) Generate Java code to evaluate the expression as a ValueRepresentation

Methods inherited from class java.lang.Object

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

Constructor Detail

ExpressionCompiler

public ExpressionCompiler()

Method Detail

compilePush

public abstract void compilePush(CompilerService compiler,
                                 Expression exp)

Generate Java code to execute the expression in push mode, that is, code to write events to the current output Receiver

Parameters:

compiler - the compiler service

exp - the expression to be compiled

compileToItem

public abstract java.lang.String compileToItem(CompilerService compiler,
                                               Expression exp)

Generate Java code to evaluate the expression as an Item

Parameters:

compiler - the compiler service

exp - the expression to be compiled

Returns:

a simple Java expression (usually the name of a variable that has been declared) which will be of class Item, and which will hold the value of the expression at run-time (or hold null, representing an empty sequence).

compileToIterator

public abstract java.lang.String compileToIterator(CompilerService compiler,
                                                   Expression exp)

Generate Java code to evaluate the expression as a SequenceIterator

Parameters:

compiler - the compiler service

exp - the XPath expression to be compiled

Returns:

a simple Java expression (usually the name of a variable that has been declared) which will be of class SequenceIterator, and which at run-time will hold an iterator over the the value of the XPath expression

compileToEffectiveBooleanValue

public abstract java.lang.String compileToEffectiveBooleanValue(CompilerService compiler,
                                                                Expression expr,
                                                                ReturnAction options)

Generate Java code to evaluate the effective boolean value of the expression

Parameters:

compiler - the compiler service

expr - the XPath expression to be compiled

options - indicates how the boolean result is to be returned

Returns:

the result depends on the supplied value of the options argument. If options is a JavaDeclaration, the code must declare a Java variable and return the name of this variable. If options is a JavaAssignment, the code must assign the value to an existing Java variable. If options is a Return, the code must generate a return statement that returns the value of the boolean (in which case the result of this method is null).

compileToCharSequence

public abstract java.lang.String compileToCharSequence(CompilerService compiler,
                                                       Expression expr)

Generate Java code to evaluate the expression as a CharSequence

Parameters:

compiler - the compiler service

expr - the XPath expression to be compiled

Returns:

a simple Java expression (usually the name of a variable that has been declared, or a string literal) which will be of class CharSequence, and which will hold the string value of the XPath expression at run-time

compileToValueRepresentation

public java.lang.String compileToValueRepresentation(CompilerService compiler,
                                                     Expression expr)

Generate Java code to evaluate the expression as a ValueRepresentation

Parameters:

compiler - the compiler service

expr - the expression to be compiled

Returns:

a simple Java expression (usually the name of a variable that has been declared) which will be of class ValueRepresentation, and which at run-time will hold the value of the expression

compileAsLoop

public void compileAsLoop(CompilerService compiler,
                          Expression expr,
                          LoopAction action)

Compile an XPath expression in the form of a loop. This generates Java code that loops over the items in the result of the expression; the body of the loop is constructed by a callback to the supplied LoopAction (which will handle nested expressions)

Parameters:

compiler - the CompilerService

expr - the XPath expression to be compiled

action - the action to be taken to compile code that processes each item in the sequence returned by the XPath expression