Class ForExpression

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

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:
  • Constructor Details

    • ForExpression

      public ForExpression()
      Create a "for" expression (for $x at $p in SEQUENCE return ACTION)
  • Method Details

    • 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)
    • 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
    • convertWhereToPredicate

      public Expression convertWhereToPredicate(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException
      Convert where clause, if possible, to a predicate.
      Parameters:
      visitor - the expression visitor
      contextItemType - the item type of the context item
      Returns:
      the converted expression if modified, or null otherwise
      Throws:
      XPathException
    • 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

      protected 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
    • 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
    • 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
    • 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