Package net.sf.saxon.expr.instruct

Class Choose

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.instruct.Instruction
net.sf.saxon.expr.instruct.Choose
All Implemented Interfaces:
ExportAgent, ConditionalInstruction, Locatable, IdentityComparable, Traceable
public class Choose extends Instruction implements ConditionalInstruction
Compiled representation of an xsl:choose or xsl:if element in the stylesheet. Also used for typeswitch in XQuery.

  • Field Details

    • CHOICE_ACTION

      public static final OperandRole CHOICE_ACTION

  • Constructor Details

    • Choose

      public Choose(Expression[] conditions, Expression[] actions)
      Construct an xsl:choose instruction
      Parameters:
      conditions - the conditions to be tested, in order
      actions - the actions to be taken when the corresponding condition is true

  • Method Details

    • makeConditional

      public static Expression makeConditional(Expression condition, Expression thenExp, Expression elseExp)
      Make a simple conditional expression (if (condition) then (thenExp) else (elseExp)
      Parameters:
      condition - the condition to be tested
      thenExp - the expression to be evaluated if the condition is true
      elseExp - the expression to be evaluated if the condition is false
      Returns:
      the expression

    • makeConditional

      public static Expression makeConditional(Expression condition, Expression thenExp)
      Make a simple conditional expression (if (condition) then (thenExp) else ()
      Parameters:
      condition - the condition to be tested
      thenExp - the expression to be evaluated if the condition is true
      Returns:
      the expression

    • setInstruction

      public void setInstruction(boolean inst)
      Say whether this choose expression originates as an XSLT instruction
      Parameters:
      inst - true if this is an xsl:choose or xsl:if instruction

    • isInstruction

      public boolean isInstruction()
      Ask whether this expression is an instruction. In XSLT streamability analysis this is used to distinguish constructs corresponding to XSLT instructions from other constructs.
      Overrides:
      isInstruction in class Instruction
      Returns:
      true if this construct originates as an XSLT instruction

    • size

      public int size()
      Get the number of branches (conditions) in the expression
      Returns:
      the number of conditions (which is the same as the number of actions)

    • isSingleBranchChoice

      public static boolean isSingleBranchChoice(Expression exp)
      Test whether an expression is a single-branch choose, that is, an expression of the form if (condition) then exp else ()
      Parameters:
      exp - the expression to be tested
      Returns:
      true if the expression is a choose expression and there is only one condition, so that the expression returns () if this condition is false

    • isActionOperand

      public boolean isActionOperand(Expression child)

    • getCondition

      public Expression getCondition(int i)
      Get the i'th condition counting from zero
      Parameters:
      i - the index of the required condition
      Returns:
      the i'th condition counting from zero

    • setCondition

      public void setCondition(int i, Expression condition)
      Set the i'th condition counting from zero
      Parameters:
      i - the index of the required condition
      condition - the new value of the i'th condition counting from zero

    • conditions

      public Iterable<Operand> conditions()
      Get the sequence of conditions
      Returns:
      all the conditions, in order

    • getActionOperand

      public Operand getActionOperand(int i)
      Get i'th action operand (counting from zero)
      Parameters:
      i - the action number (counting from zero)
      Returns:
      the i'th action to be evaluated when the corresponding condition is true

    • getAction

      public Expression getAction(int i)
      Get i'th action to be performed or evaluated (counting from zero)
      Parameters:
      i - the action number (counting from zero)
      Returns:
      the i'th action to be evaluated when the corresponding condition is true

    • setAction

      public void setAction(int i, Expression action)
      Set the i'th action counting from zero
      Parameters:
      i - the index of the required action
      action - the new value of the i'th action counting from zero

    • actions

      public Iterable<Operand> actions()
      Get the sequence of actions
      Returns:
      all the actions, in order

    • operands

      public Iterable<Operand> operands()
      Get all the operands of the Choose expresssion - that is, all the conditions and all the actions
      Specified by:
      operands in class Instruction
      Returns:
      all the operands, in undefined order.

    • allowExtractingCommonSubexpressions

      public boolean allowExtractingCommonSubexpressions()
      Ask whether common subexpressions found in the operands of this expression can be extracted and evaluated outside the expression itself. The result is irrelevant in the case of operands evaluated with a different focus, which will never be extracted in this way, even if they have no focus dependency.
      Overrides:
      allowExtractingCommonSubexpressions in class Expression
      Returns:
      false for this kind of expression

    • atomizeActions

      public void atomizeActions()
      Atomize all the action expressions

    • getInstructionNameCode

      public int getInstructionNameCode()
      Get the name of this instruction for diagnostic and tracing purposes We assume that if there was only one condition then it was an xsl:if; this is not necessarily so, but it's adequate for tracing purposes.
      Overrides:
      getInstructionNameCode in class Instruction
      Returns:
      a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace

    • simplify

      public Expression simplify() throws XPathException
      Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression).
      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

    • 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)

    • 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, Supplier<RoleDiagnostic> roleSupplier, ExpressionVisitor visitor) throws XPathException
      Static type checking for conditional expressions is delegated to the expression itself, and is performed separately on each branch of the conditional, so that dynamic checks are added only on those branches where the check is actually required. This also results in a static type error if any branch is incapable of delivering a value of the required type. One reason for this approach is to avoid doing dynamic type checking on a recursive function call as this prevents tail-call optimization being used.
      Overrides:
      staticTypeCheck in class Expression
      Parameters:
      req - the required type
      backwardsCompatible - true if backwards compatibility mode applies
      roleSupplier - 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

    • optimize

      public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo 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)

    • copy

      public Expression copy(RebindingMap rebindings)
      Copy an expression. This makes a deep copy.
      Specified by:
      copy in class Expression
      Parameters:
      rebindings - the rebinding map
      Returns:
      the copy of the original expression

    • 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

    • 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

    • 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 prefered. For instructions this is the process() method.
      Overrides:
      getImplementationMethod in class Instruction
      Returns:
      the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

    • markTailFunctionCalls

      public int markTailFunctionCalls(StructuredQName qName, int arity)
      Mark tail-recursive calls on functions. For most expressions, this does nothing.
      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.

    • getItemType

      public ItemType getItemType()
      Get the item type of the items returned by evaluating this instruction
      Overrides:
      getItemType in class Instruction
      Returns:
      the static item type of the instruction

    • 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

      protected int computeCardinality()
      Compute the cardinality of the sequence returned by evaluating this instruction
      Overrides:
      computeCardinality in class Instruction
      Returns:
      the static cardinality

    • computeSpecialProperties

      protected int computeSpecialProperties()
      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

    • mayCreateNewNodes

      public final boolean mayCreateNewNodes()
      Determine whether this instruction creates new nodes. This implementation returns true if any of the "actions" creates new nodes. (Nodes created by the conditions can't contribute to the result).
      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)

    • unordered

      public Expression unordered(boolean retainAllNodes, boolean forStreaming) throws XPathException
      Replace this expression by a simpler expression that delivers the results without regard to order.
      Overrides:
      unordered in class Expression
      Parameters:
      retainAllNodes - set to true if the result must contain exactly the same nodes as the original; set to false if the result can eliminate (or introduce) duplicates.
      forStreaming - set to true if optimizing for streaming
      Returns:
      an expression that delivers the same nodes in a more convenient order
      Throws:
      XPathException - if the rewrite fails

    • 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

    • addToPathMap

      public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
      Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

      The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.

      Overrides:
      addToPathMap in class Expression
      Parameters:
      pathMap - the PathMap to which the expression should be added
      pathMapNodeSet - the set of PathMap nodes to which the paths from this expression should be appended
      Returns:
      the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.

    • 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

    • toShortString

      public 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

    • 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.

    • evaluateItem

      public Item evaluateItem(XPathContext context) throws XPathException
      Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.
      Overrides:
      evaluateItem in class Instruction
      Parameters:
      context - The context in which the expression is to be evaluated
      Returns:
      the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression

    • iterate

      public SequenceIterator 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 relies on the process() method: it "pushes" the results of the instruction to a sequence in memory, and then iterates over this in-memory sequence.

      In principle instructions should implement a pipelined iterate() method that avoids the overhead of intermediate storage.

      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

    • getExpressionName

      public String getExpressionName()
      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.

    • getStreamerName

      public 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

    • getElaborator

      public Elaborator getElaborator()
      Make an elaborator for this expression
      Overrides:
      getElaborator in class Expression
      Returns:
      a suitable elaborator

    • getConditionEvaluators

      public BooleanEvaluator[] getConditionEvaluators()