Class FLWORExpression

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.flwor.FLWORExpression
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator

public class FLWORExpression extends Expression
This class represents a FLWOR expression, evaluated using tuple streams
See Also:
  • Field Details

  • Constructor Details

  • Method Details

    • getClauseList

      public List<Clause> getClauseList()
      Get the list of clauses of the FLWOR expression, in the order they are written. This excludes the return clause
      Returns:
      the list of clauses
    • 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
    • getReturnClause

      public Expression getReturnClause()
      Get the return clause of the FLWOR expression
      Returns:
      the expression contained in the return clause
    • hasVariableBinding

      public boolean hasVariableBinding(Binding binding)
      Determine whether a given variable binding belongs to this FLWOR expression
      Overrides:
      hasVariableBinding in class Expression
      Parameters:
      binding - the binding being sought
      Returns:
      true if this binding belongs to one of the clauses of this FLWOR expression
    • simplify

      public Expression simplify(ExpressionVisitor visitor) 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
      Parameters:
      visitor - an expression visitor
      Returns:
      the simplified expression
      Throws:
      XPathException - if an error is discovered during expression rewriting
    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException
      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.

      If the implementation returns a value other than "this", then it is required to ensure that the location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

      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)
    • implementsStaticTypeCheck

      public boolean implementsStaticTypeCheck()
      Determine whether this expression implements its own method for static type checking
      Overrides:
      implementsStaticTypeCheck in class Expression
      Returns:
      true - this expression has a non-trivial implementation of the staticTypeCheck() method
    • staticTypeCheck

      public Expression staticTypeCheck(SequenceType req, boolean backwardsCompatible, RoleLocator role, TypeCheckerEnvironment visitor) throws XPathException
      Static type checking for let expressions is delegated to the expression itself, and is performed on the "return" expression, 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
    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Determine the data type of the items returned by the expression.
      Specified by:
      getItemType in class Expression
      Parameters:
      th - the type hierarchy cache
      Returns:
      a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)
    • computeCardinality

      protected int computeCardinality()
      Compute the static cardinality of this 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
    • iterateSubExpressions

      public Iterator<Expression> iterateSubExpressions()
      Get the immediate sub-expressions of this expression.
      Overrides:
      iterateSubExpressions in class Expression
      Returns:
      an iterator containing the sub-expressions of this expression
    • checkForUpdatingSubexpressions

      public void checkForUpdatingSubexpressions() throws XPathException
      Check to ensure that this expression does not contain any inappropriate 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
    • isUpdatingExpression

      public boolean isUpdatingExpression()
      Determine whether this is an updating expression as defined in the XQuery update specification
      Overrides:
      isUpdatingExpression in class Expression
      Returns:
      true if this is an updating expression
    • replaceSubExpression

      public boolean replaceSubExpression(Expression original, Expression replacement)
      Replace one subexpression by a replacement subexpression
      Overrides:
      replaceSubExpression in class Expression
      Parameters:
      original - the original subexpression
      replacement - the replacement subexpression
      Returns:
      true if the original subexpression is found
    • 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
    • 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
    • promote

      public Expression promote(PromotionOffer offer, Expression parent) throws XPathException
      Promote this expression if possible
      Overrides:
      promote in class Expression
      Parameters:
      offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression
      parent - the containing expression in the expression tree
      Returns:
      if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
      Throws:
      XPathException - if any error is detected
    • getEvaluationMethod

      public int getEvaluationMethod()
      Overrides:
      getEvaluationMethod in class Expression
    • optimize

      public Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) 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
      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)
    • iterate

      public SequenceIterator<? extends Item> iterate(XPathContext context) throws XPathException
      Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.
      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
    • process

      public void process(XPathContext context) throws XPathException
      Process the instruction, without returning any tail calls
      Overrides:
      process in class Expression
      Parameters:
      context - The dynamic context, giving access to the current node, the current variables, etc.
      Throws:
      XPathException - if a dynamic error occurs
    • 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
      UnsupportedOperationException - if the expression is not an updating expression
    • toString

      public String toString()
      Display the expression as a string
      Overrides:
      toString in class Expression
      Returns:
      a representation of the expression as a string
    • hasLoopingVariableReference

      public boolean hasLoopingVariableReference(Binding binding)
      Determine whether a variable reference found within a clause of a FLWOR expression is a looping reference, that is, whether the variable is used more than once
      Parameters:
      binding - the variable binding, which may be bound in a clause of the same FLWOR expression, or in some containing expression
      Returns:
      true if a reference to the variable occurs within a loop relative to the binding, that is, if the variable's value is used more than once. Note that this method only detects a loop that is due to the clauses of this FLWOR expression itself. A loop in an inner expression or outer expression of the FLWOR expression must be detected by the caller.