net.sf.saxon.expr.instruct

Class Block

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.instruct.Instruction

net.sf.saxon.expr.instruct.Block

All Implemented Interfaces:

ExportAgent, TailCallReturner, Locatable, IdentityComparable

public class Block
extends Instruction

An expression that delivers the concatenation of the results of its subexpressions. This may represent an XSLT sequence constructor, or an XPath/XQuery expression of the form (a,b,c,d).

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_COST, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Constructor and Description
Block(Expression[] children) Create a block, supplying its child expressions

Method Summary

Modifier and Type	Method and Description
void	checkForUpdatingSubexpressions() Check to ensure that this expression does not contain any updating subexpressions.
void	checkPermittedContents(SchemaType parentType, boolean whole) Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type.
int	computeCardinality() Determine the cardinality of the expression
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
Expression	copy(RebindingMap rebindings) Copy an expression.
void	evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) Evaluate an updating expression, adding the results to a Pending Update List.
void	export(ExpressionPresenter out) Diagnostic print of expression structure.
java.lang.String	getExpressionName() Get a name identifying the kind of expression, in terms meaningful to a user.
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
ItemType	getItemType() Determine the data type of the items returned by this expression
Operand[]	getOperanda() Get the children of this instruction
UType	getStaticUType(UType contextItemType) Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.
java.lang.String	getStreamerName() Get the (partial) name of a class that supports streaming of this kind of expression
boolean	hasVariableBinding(Binding binding) Ask whether this expression is, or contains, the binding of a given variable
boolean	implementsStaticTypeCheck() Determine whether this expression implements its own method for static type checking
boolean	isCandidateForSharedAppend() Determine whether the block is a candidate for evaluation using a "shared append expression" where the result of the evaluation is a sequence implemented as a list of subsequences
boolean	isInstruction() Ask whether this expression is an instruction.
boolean	isVacuousExpression() Determine whether this is a vacuous expression as defined in the XQuery update specification
SequenceIterator<?>	iterate(XPathContext context) Iterate over the results of all the child expressions
static Expression	makeBlock(Expression e1, Expression e2) Static factory method to create a block.
static Expression	makeBlock(java.util.List<Expression> list) Static factory method to create a block from a list of expressions
boolean	mayCreateNewNodes() Determine whether this instruction creates new nodes.
Expression	mergeAdjacentTextInstructions() Merge any adjacent instructions that create literal text nodes
static boolean	neverReturnsTypedNodes(Instruction insn, TypeHierarchy th) Determine whether the block includes any instructions that might return nodes with a type annotation
java.lang.Iterable<Operand>	operands() Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform optimisation of an expression and its subexpressions.
TailCall	processLeavingTail(XPathContext context) ProcessLeavingTail: called to do the real work of this instruction.
Expression	simplify() Simplify an expression.
Expression	staticTypeCheck(SequenceType req, boolean backwardsCompatible, RoleDiagnostic role, ExpressionVisitor visitor) Static type checking for let expressions is delegated to the child expressions, to allow further delegation to the branches of a conditional
java.lang.String	toShortString() Produce a short string identifying the expression for use in error messages
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform type checking of an expression and its subexpressions.

Methods inherited from class net.sf.saxon.expr.instruct.Instruction

alwaysCreatesNewNodes, assembleParams, assembleTunnelParams, dynamicError, evaluateAsString, evaluateItem, getConstructType, getInstructionNameCode, getNetCost, getSourceLocator, isXSLT, process, someOperandCreatesNewNodes

Methods inherited from class net.sf.saxon.expr.Expression

addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, computeDependencies, computeHashCode, computeStaticProperties, dynamicError, effectiveBooleanValue, equals, explain, getCardinality, getConfiguration, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, hasCompatibleStaticContext, hashCode, hasSpecialProperty, identityHashCode, isCallOn, isEqual, isIdentical, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, markTailFunctionCalls, operandList, operandSparseList, optimizeChildren, prepareForStreaming, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplifyChildren, suppressValidation, toPattern, toString, typeCheckChildren, typeError, unordered, verifyParentPointers

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

Block

public Block(Expression[] children)

Create a block, supplying its child expressions

Parameters:

children - the child expressions in order

Method Detail

isInstruction

public boolean isInstruction()

Description copied from class: Expression

Ask whether this expression is an instruction. In XSLT streamability analysis this is used to distinguish constructs corresponding to XSLT instructions from other constructs, typically XPath expressions (but also things like attribute constructors on a literal result element, references to attribute sets, etc. However, an XPath expression within a text value template in a text node of an XSLT stylesheet is treated as an instruction. In a non-XSLT environment (such as XQuery) this property has no meaning and its setting is undefined.

Overrides:

isInstruction in class Instruction

Returns:

true if this construct originates as an XSLT instruction

operands

public java.lang.Iterable<Operand> operands()

Description copied from class: Expression

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()

If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

Specified by:

operands in class Instruction

Returns:

an iterator containing the sub-expressions of this expression

hasVariableBinding

public boolean hasVariableBinding(Binding binding)

Ask whether this expression is, or contains, the binding of a given variable

Overrides:

hasVariableBinding in class Expression

Parameters:

binding - the variable binding

Returns:

true if this expression is the variable binding (for example a ForExpression or LetExpression) or if it is a FLWOR expression that binds the variable in one of its clauses.

makeBlock

public static Expression makeBlock(Expression e1,
                                   Expression e2)

Static factory method to create a block. If one of the arguments is already a block, the contents will be merged into a new composite block

Parameters:

e1 - the first subexpression (child) of the block

e2 - the second subexpression (child) of the block

Returns:

a Block containing the two subexpressions, and if either of them is a block, it will have been collapsed to create a flattened sequence

makeBlock

public static Expression makeBlock(java.util.List<Expression> list)

Static factory method to create a block from a list of expressions

Parameters:

list - the list of expressions making up this block. The members of the List must be instances of Expression. The list is effectively copied; subsequent changes to the contents of the list have no effect.

Returns:

a Block containing the two subexpressions, and if either of them is a block, it will have been collapsed to create a flattened sequence

getExpressionName

public java.lang.String getExpressionName()

Description copied from class: Instruction

Get a name identifying the kind of expression, in terms meaningful to a user.

Overrides:

getExpressionName in class Instruction

Returns:

a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.

getOperanda

public Operand[] getOperanda()

Get the children of this instruction

Returns:

the children of this instruction, as an array of Operand objects. May return a zero-length array if there are no children.

computeSpecialProperties

public int computeSpecialProperties()

Description copied from class: Instruction

Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Overrides:

computeSpecialProperties in class Instruction

Returns:

a set of flags indicating static properties of this expression

implementsStaticTypeCheck

public boolean implementsStaticTypeCheck()

Description copied from class: Expression

Determine whether this expression implements its own method for static type checking

Overrides:

implementsStaticTypeCheck in class Expression

Returns:

true if this expression has a non-trivial implementation of the staticTypeCheck() method

staticTypeCheck

public Expression staticTypeCheck(SequenceType req,
                                  boolean backwardsCompatible,
                                  RoleDiagnostic role,
                                  ExpressionVisitor visitor)
                           throws XPathException

Static type checking for let expressions is delegated to the child expressions, to allow further delegation to the branches of a conditional

Overrides:

staticTypeCheck in class Expression

Parameters:

req - the required type

backwardsCompatible - true if backwards compatibility mode applies

role - the role of the expression in relation to the required type

visitor - an expression visitor

Returns:

the expression after type checking (perhaps augmented with dynamic type checking code)

Throws:

XPathException - if failures occur, for example if the static type of one branch of the conditional is incompatible with the required type

neverReturnsTypedNodes

public static boolean neverReturnsTypedNodes(Instruction insn,
                                             TypeHierarchy th)

Determine whether the block includes any instructions that might return nodes with a type annotation

Parameters:

insn - the instruction (for example this block)

th - the type hierarchy cache

Returns:

true if any expression in the block can return type-annotated nodes

mergeAdjacentTextInstructions

public Expression mergeAdjacentTextInstructions()

Merge any adjacent instructions that create literal text nodes

Returns:

the expression after merging literal text instructions

copy

public Expression copy(RebindingMap rebindings)

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Parameters:

rebindings - Variables that need to be re-bound

Returns:

the copy of the original expression

getItemType

public final ItemType getItemType()

Determine the data type of the items returned by this expression

Overrides:

getItemType in class Instruction

Returns:

the data type

getStaticUType

public UType getStaticUType(UType contextItemType)

Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.

Overrides:

getStaticUType in class Expression

Parameters:

contextItemType - the static type of the context item

Returns:

the static item type of the expression according to the XSLT 3.0 defined rules

computeCardinality

public int computeCardinality()

Determine the cardinality of the expression

Overrides:

computeCardinality in class Instruction

Returns:

the static cardinality

mayCreateNewNodes

public final boolean mayCreateNewNodes()

Determine whether this instruction creates new nodes. This implementation returns true if any child instruction returns true.

Overrides:

mayCreateNewNodes in class Instruction

Returns:

true if the instruction creates new nodes under some input conditions (or if it can't be proved that it doesn't)

checkForUpdatingSubexpressions

public void checkForUpdatingSubexpressions()
                                    throws XPathException

Check to ensure that this expression does not contain any updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.

Overrides:

checkForUpdatingSubexpressions in class Expression

Throws:

XPathException - if the expression has a non-permitted updateing subexpression

isVacuousExpression

public boolean isVacuousExpression()

Determine whether this is a vacuous expression as defined in the XQuery update specification

Overrides:

isVacuousExpression in class Expression

Returns:

true if this expression is vacuous

simplify

public Expression simplify()
                    throws XPathException

Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

Overrides:

simplify in class Expression

Returns:

the simplified expression (or the original if unchanged, or if modified in-situ)

Throws:

XPathException - if an error is discovered during expression rewriting

isCandidateForSharedAppend

public boolean isCandidateForSharedAppend()

Determine whether the block is a candidate for evaluation using a "shared append expression" where the result of the evaluation is a sequence implemented as a list of subsequences

Returns:

true if the block is a candidate for "shared append" processing

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ContextItemStaticInfo contextInfo)
                     throws XPathException

Description copied from class: Expression

Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

Overrides:

typeCheck in class Expression

Parameters:

visitor - an expression visitor

contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.

Returns:

the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ContextItemStaticInfo contextInfo)
                    throws XPathException

Description copied from class: Expression

Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

Overrides:

optimize in class Expression

Parameters:

visitor - an expression visitor

contextInfo - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE

Returns:

the original expression, rewritten if appropriate to optimize execution

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

checkPermittedContents

public void checkPermittedContents(SchemaType parentType,
                                   boolean whole)
                            throws XPathException

Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.

Overrides:

checkPermittedContents in class Expression

Parameters:

parentType - the "given complex type": the method is checking that the nodes returned by this expression are acceptable members of the content model of this type

whole - if true, we want to check that the value of this expression satisfies the content model as a whole; if false we want to check that the value of the expression is acceptable as one part of the content

Throws:

XPathException - if the value delivered by this expression cannot be part of the content model of the given type

export

public void export(ExpressionPresenter out)
            throws XPathException

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

export in interface ExportAgent

Specified by:

export in class Expression

Parameters:

out - the expression presenter used to display the structure

Throws:

XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

toShortString

public java.lang.String toShortString()

Description copied from class: Expression

Produce a short string identifying the expression for use in error messages

Overrides:

toShortString in class Expression

Returns:

a short string, sufficient to identify the expression

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException

Description copied from class: Instruction

ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.

Specified by:

processLeavingTail in interface TailCallReturner

Specified by:

processLeavingTail in class Instruction

Parameters:

context - The dynamic context of the transformation, giving access to the current node, the current variables, etc.

Returns:

null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.

Throws:

XPathException - if a dynamic error occurs during the evaluation of the instruction

getImplementationMethod

public int getImplementationMethod()

An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided. This implementation provides both iterate() and process() methods natively.

Overrides:

getImplementationMethod in class Instruction

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

iterate

public SequenceIterator<?> iterate(XPathContext context)
                            throws XPathException

Iterate over the results of all the child expressions

Overrides:

iterate in class Instruction

Parameters:

context - supplies the context for evaluation

Returns:

a SequenceIterator that can be used to iterate over the result of the expression

Throws:

XPathException - if any dynamic error occurs evaluating the expression

evaluatePendingUpdates

public void evaluatePendingUpdates(XPathContext context,
                                   PendingUpdateList pul)
                            throws XPathException

Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException

Overrides:

evaluatePendingUpdates in class Expression

Parameters:

context - the XPath dynamic evaluation context

pul - the pending update list to which the results should be written

Throws:

XPathException - if evaluation fails

getStreamerName

public java.lang.String getStreamerName()

Description copied from class: Expression

Get the (partial) name of a class that supports streaming of this kind of expression

Overrides:

getStreamerName in class Expression

Returns:

the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class