## net.sf.saxon.expr
Class ForExpression

    java.lang.Object
      net.sf.saxon.expr.Expression
          net.sf.saxon.expr.Assignation
              net.sf.saxon.expr.ForExpression

All Implemented Interfaces:
  Serializable, SourceLocator, LocationProvider, SaxonLocator, Binding, EvaluableItem, SequenceIterable, InstructionInfo, Locator

Direct Known Subclasses:
  OuterForExpression

    public class ForExpression

extends Assignation

A ForExpression maps an expression over a sequence. This version works with range variables, it doesn't change the context information

See Also:
  Serialized Form

Nested Class Summary
`protected static class` `ForExpression.EventMappingAction` The EventMappingAction represents the action to be taken for each item in the source sequence.
`protected static class` `ForExpression.MappingAction` The MappingAction represents the action to be taken for each item in the source sequence.

Field Summary
`protected PositionVariable` `positionVariable`

Fields inherited from class net.sf.saxon.expr.Assignation
`action, requiredType, sequence, slotNumber, variableName`

Fields inherited from class net.sf.saxon.expr.Expression
`EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, PUSH_SELECTION, staticProperties, WATCH_METHOD`

Constructor Summary
`ForExpression()` Create a "for" expression (for $x at $p in SEQUENCE return ACTION)

Method Summary
`void` `checkPermittedContents(SchemaType parentType, StaticContext env, 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 static cardinality of the expression
`Expression` `copy()` Copy an expression.
`void` `evaluatePendingUpdates(XPathContext context, PendingUpdateList pul)` Evaluate an updating expression, adding the results to a Pending Update List.
`void` `explain(ExpressionPresenter out)` Diagnostic print of expression structure.
`protected void` `explainSpecializedAttributes(ExpressionPresenter out)`
`Binding[]` `extendBindingList(Binding[] in)` Extend an array of variable bindings to include the binding(s) defined in this expression
`int` `getConstructType()` Get the type of this expression for use in tracing and diagnostics
`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(TypeHierarchy th)` Determine the data type of the items returned by the expression, if possible
`StructuredQName` `getPositionVariableName()` Get the name of the position variable
`protected int` `getRangeVariableCardinality()` Get the cardinality of the range variable
`int` `getRequiredSlots()` Get the number of slots required.
`boolean` `hasLoopingSubexpression(Expression child)` Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
`boolean` `isVacuousExpression()` Determine whether this is a vacuous expression as defined in the XQuery update specification
`SequenceIterator` `iterate(XPathContext context)` Iterate over the sequence of values
`EventIterator` `iterateEvents(XPathContext context)` Deliver the result of the expression as a sequence of events.
`int` `markTailFunctionCalls(StructuredQName qName, int arity)` Mark tail function calls: only possible if the for expression iterates zero or one times.
`Expression` `optimize(ExpressionVisitor visitor, ItemType contextItemType)` Optimize the expression
`void` `process(XPathContext context)` Process this expression as an instruction, writing results to the current outputter
`void` `setPositionVariable(PositionVariable decl)` Set the reference to the position variable (XQuery only)
`void` `setSlotNumber(int nr)` Set the slot number for the range variable
`String` `toString()` The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
`Expression` `typeCheck(ExpressionVisitor visitor, ItemType contextItemType)` Type-check the expression

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

`addReference, addToPathMap, checkForUpdatingSubexpressions, evaluateVariable, getAction, getLocalSlotNumber, getNominalReferenceCount, getObjectName, getRequiredType, getSequence, getVariableName, getVariableQName, isAssignable, isGlobal, isIndexedVariable, isUpdatingExpression, iterateSubExpressions, promote, promoteWhereClause, refineTypeInformation, replaceSubExpression, replaceVariable, setAction, setIndexedVariable, setRequiredType, setSequence, setVariableQName, simplify, suppressValidation`

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

`adoptChildExpression, computeDependencies, computeSpecialProperties, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, getCardinality, getColumnNumber, getColumnNumber, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, implementsStaticTypeCheck, isSubtreeExpression, iterateSameFocusSubExpressions, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, typeError`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Field Detail

### positionVariable

    protected PositionVariable positionVariable

Constructor Detail

### ForExpression

    public ForExpression()

  Create a "for" expression (for $x at $p in SEQUENCE return ACTION)

Method Detail

### getExpressionName

    public String getExpressionName()

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

  Overrides:
    `getExpressionName` in class `Expression`
  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.

### setPositionVariable

    public void setPositionVariable(PositionVariable decl)

  Set the reference to the position variable (XQuery only)

  Parameters:
    `decl` - the range variable declaration for the position variable

### getPositionVariableName

    public StructuredQName getPositionVariableName()

  Get the name of the position variable

  Returns:
    the name of the position variable ("at $p") if there is one, or null if not

### setSlotNumber

    public void setSlotNumber(int nr)

  Set the slot number for the range variable

  Overrides:
    `setSlotNumber` in class `Assignation`
  Parameters:
    `nr` - the slot number allocated to the range variable on the local stack frame. This implicitly allocates the next slot number to the position variable if there is one.

### getRequiredSlots

    public int getRequiredSlots()

  Get the number of slots required.

  Overrides:
    `getRequiredSlots` in class `Assignation`
  Returns:
    normally 1, except for a FOR expression with an AT clause, where it is 2.

### typeCheck

    public Expression typeCheck(ExpressionVisitor visitor,
                                ItemType contextItemType)
                         throws XPathException

  Type-check the expression

  Overrides:
    `typeCheck` in class `Expression`
  Parameters:
    `visitor` - an expression visitor
    `contextItemType` - 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 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)

### getRangeVariableCardinality

    protected int getRangeVariableCardinality()

  Get the cardinality of the range variable

  Returns:
    the cardinality of the range variable (StaticProperty.EXACTLY_ONE). Can be overridden in a subclass

### optimize

    public Expression optimize(ExpressionVisitor visitor,
                               ItemType contextItemType)
                        throws XPathException

  Optimize the expression

  Overrides:
    `optimize` in class `Expression`
  Parameters:
    `visitor` - an expression visitor
    `contextItemType` - 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)

### hasLoopingSubexpression

    public boolean hasLoopingSubexpression(Expression child)

  Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly

  Overrides:
    `hasLoopingSubexpression` in class `Expression`
  Parameters:
    `child` - the immediate subexpression
  Returns:
    true if the child expression is evaluated repeatedly

### copy

    public Expression copy()

  Copy an expression. This makes a deep copy.

  Specified by:
    `copy` in class `Expression`
  Returns:
    the copy of the original expression

### markTailFunctionCalls

    public int markTailFunctionCalls(StructuredQName qName,
                                     int arity)

  Mark tail function calls: only possible if the for expression iterates zero or one times. (This arises in XSLT/XPath, which does not have a LET expression, so FOR gets used instead)

  Overrides:
    `markTailFunctionCalls` in class `Expression`
  Parameters:
    `qName` - the name of the function
    `arity` - the arity (number of parameters) of the function
  Returns:
    0 if no tail call was found; 1 if a tail call on a different function was found; 2 if a tail recursive call was found and if this call accounts for the whole of the value.

### extendBindingList

    public Binding[] extendBindingList(Binding[] in)

  Extend an array of variable bindings to include the binding(s) defined in this expression

  Overrides:
    `extendBindingList` in class `Assignation`
  Parameters:
    `in` - a set of variable bindings
  Returns:
    a set of variable bindings including all those supplied plus this one

### 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

### 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 `Expression`
  Returns:
    the implementation method, for example `Expression.ITERATE_METHOD` or `Expression.EVALUATE_METHOD` or `Expression.PROCESS_METHOD`

### checkPermittedContents

    public void checkPermittedContents(SchemaType parentType,
                                       StaticContext env,
                                       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
    `env` - the static context
    `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

### iterate

    public SequenceIterator iterate(XPathContext context)
                             throws XPathException

  Iterate over the sequence of values

  Specified by:
    `iterate` in interface `SequenceIterable`
  Overrides:
    `iterate` in class `Expression`
  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

### iterateEvents

    public EventIterator iterateEvents(XPathContext context)
                                throws XPathException

  Deliver the result of the expression as a sequence of events.

  Overrides:
    `iterateEvents` in class `Expression`
  Parameters:
    `context` - The dynamic evaluation context
  Returns:
    the result of the expression as an iterator over a sequence of PullEvent objects
  Throws:
    `XPathException` - if a dynamic error occurs during expression evaluation

### process

    public void process(XPathContext context)
                 throws XPathException

  Process this expression as an instruction, writing results to the current outputter

  Overrides:
    `process` in class `Expression`
  Parameters:
    `context` - The dynamic context, giving access to the current node, the current variables, etc.
  Throws:
    `XPathException`

### 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`

### getItemType

    public ItemType getItemType(TypeHierarchy th)

  Determine the data type of the items returned by the expression, if possible

  Specified by:
    `getItemType` in class `Expression`
  Parameters:
    `th` - the type hierarchy cache
  Returns:
    one of the values Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known in advance)

### computeCardinality

    public int computeCardinality()

  Determine the static cardinality of the expression

  Specified by:
    `computeCardinality` in class `Expression`
  Returns:
    the computed cardinality, as one of the values `StaticProperty.ALLOWS_ZERO_OR_ONE`, `StaticProperty.EXACTLY_ONE`, `StaticProperty.ALLOWS_ONE_OR_MORE`, `StaticProperty.ALLOWS_ZERO_OR_MORE`

### toString

    public String toString()

  The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

  Overrides:
    `toString` in class `Expression`
  Returns:
    a representation of the expression as a string

### explain

    public void explain(ExpressionPresenter out)

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

  Specified by:
    `explain` in class `Expression`
  Parameters:
    `out` - the expression presenter used to display the structure

### explainSpecializedAttributes

    protected void explainSpecializedAttributes(ExpressionPresenter out)

### getConstructType

    public int getConstructType()

  Get the type of this expression for use in tracing and diagnostics

  Specified by:
    `getConstructType` in interface `InstructionInfo`
  Overrides:
    `getConstructType` in class `Expression`
  Returns:
    the type of expression, as enumerated in class `Location`

Copyright (c) 2004-2010 Saxonica Limited. All rights reserved.