# Package net.sf.saxon.expr

This package provides classes associated with XPath expression handling. Generally, these classes are not intended to be used directly by user-written applications; the API for XPath evaluation is now provided by classes in the package `net.sf.saxon.xpath`

The principal classes are:

Expression:
This represents an XPath Expression. There is a static method Expression.make() which is used to construct an Expression from a String (it is a factory method rather than a constructor, because it typically returns some subclass of Expression according to the syntax supplied). Subclasses of Expression represent different kinds of expression such as StringExpression and BooleanExpression. What they all have in common is an evaluate() method, which evaluates the expression in a given context to yield a Value, and an iterate() method, which treats the result of the expression as a sequence, and iterates over the items in the sequence.

ExpressionParser:
This class does the work of parsing both Expressions and Patterns. Applications should not call it directly. It uses the class Tokenizer for lexical analysis.

StaticContext:
This interface defines the information available at the time an expression is being parsed. This includes the names of variables, the bindings of namespace prefixes, the functions that are available, the names of collating sequences, and so on. When an XPath expression appears in a stylesheet, the class `net.sf.saxon.style.ExpressionContext` provides the StaticContext. For a free-standing XPath expression, the class `net.sf.saxon.xpath.StandaloneContext` is available, though a user-written class that implements `StaticContext` can also be used.

XPathContext:
This class defines the context information available at run-time, for example the context node, position, and size. (It actually does this by wrapping a SequenceIterator that represents the current sequence.) When expressions are used during an XSLT transformation, the XPathContext also provides access to the Controller, which contains all the context information about XSLT processing (for example the current template, the current group, and so on).

Most of the classes in this package represent individual syntactic constructs found in XPath or XQuery expressions: for example `ValueComparison`, `UserFunctionCall`, and `RootExpression`. The objects that instantiate these classes form the nodes on the Abstract Syntax Tree constructed by the compiler and modified by the optimizer; at run-time their methods are used to drive a pipelined evaluation of the expression.

The distinction between the compiled form of XSLT instructions and the compiled form of XPath expressions has become blurred. Generally, the compiled form of instructions is in the package `net.sf.saxon.instruct` (this includes expressions in XQuery that are equivalent to XSLT instructions, for example element constructors). However, some constructs such as conditional expressions now exist in both languages and may generate the same run-time constructs.

- Interface Summary
  Interface | Description
  --- | ---
  Binding | Binding is a interface used to represent the run-time properties and methods associated with a variable: specifically, a method to get the value of the variable.
  BindingReference | BindingReference is a interface used to mark references to a variable declaration.
  Callable | A generic interface for calling expressions by supplying the values of their subexpressions
  ComparisonExpression | Interface implemented by expressions that perform a comparison
  ComponentInvocation | Represents an expression or instruction such as call-template, or a user function call, or a global variable reference, that needs to be bound to a target component, and can potentially be re-bound when the containing component is copied into another package.
  ContextMappingFunction | ContextMappingFunction is an interface that must be satisfied by an object passed to a ContextMappingIterator.
  ContextOriginator | Represents a construct that is responsible for originating a new context; used in analysing the stack of context objects for diagnostics
  ContextSwitchingExpression | Interface implemented by expressions that switch the context, for example A/B or A[B]
  ExportAgent | An export agent performs the job of exporting an expression to a SEF file.
  ExpressionOwner | Abstraction representing any class that can act as the container for an expression: either an Operand of a parent expression, or a top-level construct such as a function or template or XQuery expression
  ItemMappingFunction | ItemMappingFunction is an interface that must be satisfied by an object passed to a ItemMappingIterator.
  LastPositionFinder | A LastPositionFinder is an interface implemented by any SequenceIterator that is able to return the position of the last item in the sequence.
  LocalBinding | Binding for local variables and parameters: anything that is allocated a slot on the XPathContext stack frame.
  Locatable | Represents a construct that has a meaningful location for use in diagnostics
  MappingFunction | MappingFunction is an interface that must be satisfied by an object passed to a MappingIterator.
  Negatable | This interface is implemented by expressions that returns a boolean value, and returns an expression whose result is the negated boolean value
  PendingUpdateList | A PendingUpdateList is created by updating expressions in XQuery Update.
  StaticContext | A StaticContext contains the information needed while an expression or pattern is being parsed.
  TailCallLoop.TailCallInfo |
  UserFunctionResolvable | A reference to a function; typically a forwards reference to a user-defined function in XQuery that has not yet been compiled.
  XPathContext | This class represents a context in which an XPath expression is evaluated.

- Class Summary
  Class | Description
  --- | ---
  AdjacentTextNodeMerger | This class performs the first phase of processing in "constructing simple content": it takes an input sequence, eliminates empty text nodes, and combines adjacent text nodes into one.
  AnalyzeMappingFunction | Mapping function that maps the sequence of matching/non-matching strings to the sequence delivered by applying the matching-substring and non-matching-substring expressions respectively to each such string
  AndExpression |
  ArithmeticExpression | Arithmetic Expression: an expression using one of the operators plus, minus, multiply, div, idiv, mod.
  Assignation | Assignation is an abstract superclass for the kinds of expression that declare range variables: for, some, and every.
  AtomicSequenceConverter | An AtomicSequenceConverter is an expression that performs a cast (or other supplied conversion) on each member of a supplied sequence
  AtomicSequenceConverter.AtomicSequenceMappingFunction | Mapping function wrapped around a converter
  AtomicSequenceConverter.ToStringMappingFunction | Mapping function that converts every item in a sequence to a string
  Atomizer | An Atomizer is an expression corresponding essentially to the fn:data() function: it maps a sequence by replacing nodes with their typed values
  AttributeGetter | An AttributeGetter is an expression that returns the value of a specific attribute of the context item, provided that it is an untyped element node.
  AxisAtomizingIterator | This iterator returns a sequence of atomic values, the result of atomizing the sequence of nodes returned by an underlying SequenceIterator.
  AxisExpression | An AxisExpression is always obtained by simplifying a PathExpression.
  BigRangeIterator | An Iterator that produces numeric values in a monotonic sequence, where the integers may exceed the range of a Long
  BinaryExpression | Binary Expression: a numeric or boolean expression consisting of the two operands and an operator
  BooleanExpression | Boolean expression: two truth values combined using AND or OR.
  Calculator | This class evaluates arithmetic expressions; it acts as a helper class to the ArithmeticExpression class.
  Calculator.AnyDivAny | Arithmetic: anyAtomicType div AnyAtomicType
  Calculator.AnyIdivAny | Arithmetic: anyAtomicType idiv AnyAtomicType
  Calculator.AnyMinusAny | Arithmetic: anyAtomicType - AnyAtomicType
  Calculator.AnyModAny | Arithmetic: anyAtomicType mod AnyAtomicType
  Calculator.AnyPlusAny | Arithmetic: anyAtomicType + AnyAtomicType
  Calculator.AnyTimesAny | Arithmetic: anyAtomicType * AnyAtomicType
  Calculator.DecimalDivDecimal | Arithmetic: decimal div decimal (including types that promote to decimal, that is, integer)
  Calculator.DecimalIdivDecimal | Arithmetic: decimal idiv decimal (including types that promote to decimal, that is, integer)
  Calculator.DecimalMinusDecimal | Arithmetic: decimal - decimal (including types that promote to decimal, that is, integer)
  Calculator.DecimalModDecimal | Arithmetic: decimal mod decimal (including types that promote to decimal, that is, integer)
  Calculator.DecimalPlusDecimal | Arithmetic: decimal + decimal (including types that promote to decimal, that is, integer)
  Calculator.DecimalTimesDecimal | Arithmetic: decimal * decimal (including types that promote to decimal, that is, integer)
  Calculator.DoubleDivDouble | Arithmetic: double div double (including types that promote to double)
  Calculator.DoubleMinusDouble | Arithmetic: double - double (including types that promote to double)
  Calculator.DoubleModDouble | Arithmetic: double mod double (including types that promote to double)
  Calculator.DoublePlusDouble | Arithmetic: double + double (including types that promote to double)
  Calculator.DoubleTimesDouble | Arithmetic: double * double (including types that promote to double)
  Calculator.FloatDivFloat | Arithmetic: float div float (including types that promote to float)
  Calculator.FloatIdivFloat | Arithmetic: float idiv float (including types that promote to float)
  Calculator.FloatMinusFloat | Arithmetic: float - float (including types that promote to float)
  Calculator.FloatModFloat | Arithmetic: float mod float (including types that promote to float)
  Calculator.FloatPlusFloat | Arithmetic: float + float (including types that promote to float)
  Calculator.FloatTimesFloat | Arithmetic: float * float (including types that promote to float)
  Calculator.IntegerDivInteger | Arithmetic: integer div integer
  Calculator.IntegerIdivInteger | Arithmetic: integer idiv integer
  Calculator.IntegerMinusInteger | Arithmetic: integer - integer
  Calculator.IntegerModInteger | Arithmetic: integer mod integer
  Calculator.IntegerPlusInteger | Arithmetic: integer + integer
  Calculator.IntegerTimesInteger | Arithmetic: integer * integer
  CardinalityChecker | A CardinalityChecker implements the cardinality checking of "treat as": that is, it returns the supplied sequence, checking that its cardinality is correct
  CardinalityCheckingIterator | CardinalityCheckingIterator returns the items in an underlying sequence unchanged, but checks that the number of items conforms to the required cardinality.
  CastableExpression | Castable Expression: implements "Expr castable as atomic-type?".
  CastExpression | Cast Expression: implements "cast as data-type ( expression )".
  CastingExpression | Casting Expression: abstract superclass for "cast as X" and "castable as X", which share a good deal of logic
  CompareToConstant | This class implements a comparison of a computed value to a literal constant using one of the operators eq, ne, lt, gt, le, ge.
  CompareToIntegerConstant | This class implements a comparison of a numeric value to an integer constant using one of the operators eq, ne, lt, gt, le, ge.
  CompareToStringConstant | This class implements a comparison of a computed value to a string constant using one of the operators eq, ne, lt, gt, le, ge.
  Component | Represents a component as defined in the XSLT 3.0 specification: for example a function, a named template, an attribute set, a global variable.
  Component.M |
  ComponentBinding | A ComponentBinding is a reference from one component to another; for example a variable reference or function call.
  ConsumingOperand | This expression is used as a proxy for the consuming operand of an expression such as an arithmetic expression for which there is no explicit streaming support.
  ContextItemExpression | This class represents the expression "(dot)", which always returns the context item.
  ContextMappingIterator | ContextMappingIterator merges a sequence of sequences into a single flat sequence.
  CurrentItemExpression | The expression is generated when compiling the current() function in XSLT.
  DifferenceEnumeration | An enumeration representing a nodeset that is teh difference of two other NodeSets.
  EagerLetExpression | An EagerLetExpression is the same as a LetExpression except that the variable is evaluated using eager evaluation rather than lazy evaluation.
  EarlyEvaluationContext | This class is an implementation of XPathContext used when evaluating constant sub-expressions at compile time.
  EmptyTextNodeRemover | This class performs part of the processing in "constructing simple content": it takes an input sequence and eliminates empty text nodes into one.
  EquivalenceComparer | A comparer that compares atomic values for equality, with the properties: - non-comparable types compare false - NaN compares equal to NaN
  EquivalenceComparison | Class to handle equivalence comparisons of singletons.
  ErrorExpression | Error expression: this expression is generated when the supplied expression cannot be parsed, and the containing element enables forwards-compatible processing.
  ErrorIterator | A SequenceIterator that throws an exception as soon as its next() method is called.
  Expression | Interface supported by an XPath expression.
  FilterExpression | A FilterExpression contains a base expression and a filter predicate, which may be an integer expression (positional filter), or a boolean expression (qualifier)
  FilterIterator | A FilterIterator filters an input sequence using a filter expression.
  FilterIterator.NonNumeric | Subclass to handle the common special case where it is statically known that the filter cannot return a numeric value
  FirstItemExpression | A FirstItemExpression returns the first item in the sequence returned by a given base expression
  ForExpression | A ForExpression maps an expression over a sequence.
  ForExpression.MappingAction | The MappingAction represents the action to be taken for each item in the source sequence.
  FunctionCall | Abstract superclass for calls to system-defined and user-defined functions
  GeneralComparison | GeneralComparison: a boolean expression that compares two expressions for equals, not-equals, greater-than or less-than.
  GeneralComparison20 | The class GeneralComparison20 specializes GeneralComparison for the case where the comparison is done with 2.0 semantics (i.e.
  GlobalVariableReference | A reference to a global variable
  HomogeneityChecker | This class is an expression that does a run-time check of the result of a "/" expression to ensure that (a) the results consists entirely of atomic values and function items, or entirely of nodes, and (b) if the results are nodes, then they are deduplicated and sorted into document order.
  IdentityComparison | IdentityComparison: a boolean expression that compares two nodes for equals, not-equals, greater-than or less-than based on identity and document ordering
  InstanceOfExpression | InstanceOf Expression: implements "Expr instance of data-type"
  IntegerRangeTest | An IntegerRangeTest is an expression of the form E = N to M where N and M are both expressions of type integer.
  IntersectionEnumeration | An enumeration representing a nodeset that is an intersection of two other NodeSets.
  IsLastExpression | A position() eq last() expression, generated by the optimizer.
  ItemChecker | A ItemChecker implements the item type checking of "treat as": that is, it returns the supplied sequence, checking that all its items are of the correct type
  ItemMappingIterator | ItemMappingIterator applies a mapping function to each item in a sequence.
  ItemTypeCheckingFunction | A mapping function for use in conjunction with an `ItemMappingIterator` that checks that all the items in a sequence are instances of a given item type
  JPConverter | This class together with its embedded subclasses handles conversion from Java values to XPath values.
  JPConverter.ExternalObjectWrapper |
  JPConverter.FromBigDecimal |
  JPConverter.FromBigInteger |
  JPConverter.FromBoolean |
  JPConverter.FromBooleanArray |
  JPConverter.FromByte |
  JPConverter.FromByteArray |
  JPConverter.FromCharacter |
  JPConverter.FromCharArray |
  JPConverter.FromCollection |
  JPConverter.FromDate |
  JPConverter.FromDouble |
  JPConverter.FromDoubleArray |
  JPConverter.FromFloat |
  JPConverter.FromFloatArray |
  JPConverter.FromInstant |
  JPConverter.FromInt |
  JPConverter.FromIntArray |
  JPConverter.FromLocalDate |
  JPConverter.FromLocalDateTime |
  JPConverter.FromLong |
  JPConverter.FromLongArray |
  JPConverter.FromObject |
  JPConverter.FromObjectArray |
  JPConverter.FromOffsetDateTime |
  JPConverter.FromQName |
  JPConverter.FromSequence |
  JPConverter.FromSequenceIterator |
  JPConverter.FromShort |
  JPConverter.FromShortArray |
  JPConverter.FromSource |
  JPConverter.FromString |
  JPConverter.FromURI |
  JPConverter.FromXdmValue |
  JPConverter.FromZonedDateTime |
  JPConverter.VoidConverter |
  LastItemExpression | A LastItemExpression returns the last item in the sequence returned by a given base expression.
  LetExpression | A LetExpression represents the XQuery construct let $x := expr return expr.
  ListCastableFunction | A function item representing a castability test for a list type
  ListConstructorFunction | A function item representing a constructor function for a list type
  Literal | A Literal is an expression whose value is constant: it is a class that implements the `Expression` interface as a wrapper around a `GroundedValue`.
  LocalVariableReference | Variable reference: a reference to a local variable.
  LookupAllExpression | A lookup expression is an expression of the form A?*, where A must be a map or an array
  LookupExpression | A lookup expression is an expression of the form A?B.
  MappingIterator | MappingIterator merges a sequence of sequences into a single flat sequence.
  MultiIterator<T> | An iterator that combines the results of a sequence of iterators
  NegateExpression | Negate Expression: implements the unary minus operator.
  NumberSequenceFormatter | This expression performs the formatting part of the logic of the xsl:number instruction It takes as input a sequence of integers, which may either be supplied directly as the value attribute of xsl:number, or may be computed by counting nodes.
  Operand | Information about a sub-expression and its relationship to the parent expression
  OperandRole | Defines the role of a child expression relative to its parent expression.
  OrExpression |
  PackageData | Information about a unit of compilation: in XSLT, a package; in XQuery, a module.
  PJConverter | This class together with its embedded subclasses handles conversion from XPath values to Java values
  PJConverter.AnyURIValueToURI |
  PJConverter.AnyURIValueToURL |
  PJConverter.Atomic | Converter for use when the source object is an atomic value, but nothing more is known statically.
  PJConverter.BooleanValueToBoolean |
  PJConverter.CalendarValueToCalendar |
  PJConverter.CalendarValueToDate |
  PJConverter.CalendarValueToInstant |
  PJConverter.CalendarValueToLocalDateTime |
  PJConverter.CalendarValueToOffsetDateTime |
  PJConverter.CalendarValueToZonedDateTime |
  PJConverter.DateValueToLocalDate |
  PJConverter.General | General-purpose converter when nothing more specific is available.
  PJConverter.Identity |
  PJConverter.IntegerValueToBigInteger |
  PJConverter.IntegerValueToByte |
  PJConverter.IntegerValueToChar |
  PJConverter.IntegerValueToInt |
  PJConverter.IntegerValueToLong |
  PJConverter.IntegerValueToShort |
  PJConverter.NumericValueToBigDecimal |
  PJConverter.NumericValueToDouble |
  PJConverter.NumericValueToFloat |
  PJConverter.QualifiedNameValueToQName |
  PJConverter.StringValueToChar |
  PJConverter.StringValueToString |
  PJConverter.ToArray | Converter for use when the target class is an array
  PJConverter.ToCollection | Converter for use when the target class is a collection class.
  PJConverter.ToNull |
  PJConverter.ToOne | Converter for use when the target class is `One`, which constrains the value to be a singleton
  PJConverter.ToOneOrMore | Converter for use when the target class is `OneOrMore`, which constrains the value to be a non-empty sequence
  PJConverter.ToSequenceExtent |
  PJConverter.ToSequenceIterator |
  PJConverter.ToZeroOrMore | Converter for use when the target class is `ZeroOrMore`, which allows any sequence but is a generic (parameterized) class so there is compile-time information about the type of items
  PJConverter.ToZeroOrOne | Converter for use when the target class is `ZeroOrOne`, which constrains the value to be a singleton or an empty sequence
  PJConverter.UnwrapExternalObject |
  PseudoExpression | A pseudo-expression is an object that can appear as a node on the expression tree, but which cannot actually be evaluated in its own right.
  QuantifiedExpression | A QuantifiedExpression tests whether some/all items in a sequence satisfy some condition.
  RangeExpression | A RangeExpression is an expression that represents an integer sequence as a pair of end-points (for example "x to y").
  RangeIterator | An Iterator that produces numeric values in a monotonic sequence, ascending or descending.
  ReverseRangeIterator | Iterator that produces numeric values in a monotonic sequence, ascending or descending.
  RootExpression | An expression whose value is always a set of nodes containing a single node, the document root.
  SimpleExpression | An abstract implementation of Expression designed to make it easy to implement new expressions, in particular, expressions to support extension instructions.
  SimpleStepExpression | A SimpleStepExpression is a special case of a SlashExpression in which the start expression selects a single item (or nothing), and the step expression is a simple AxisExpression.
  SingleItemFilter | A SingleItemFilter is an expression that selects zero or one items from a supplied sequence
  SingletonAtomizer | A SingletonAtomizer combines the functions of an Atomizer and a CardinalityChecker: it is used to atomize a sequence of nodes, checking that the result of the atomization contains zero or one atomic values.
  SingletonIntersectExpression | This expression is equivalent to (A intersect B) in the case where A has cardinality zero-or-one.
  SlashExpression | A slash expression is any expression using the binary slash operator "/".
  StackFrame | This class represents a stack frame holding details of the variables used in a function or in an XSLT template.
  StaticFunctionCall | A call to a function that is known statically.
  StaticProperty | This class contains constants identifying dependencies that an XPath expression might have on its context.
  StringLiteral | Subclass of Literal used specifically for string literals, as this is a common case
  SubscriptExpression | A SubscriptExpression represents a FilterExpression of the form EXPR[n] where n is known to be singleton numeric and to be independent of the focus; it does not need to be constant
  SubsequenceIterator | A SubsequenceIterator selects a subsequence of a sequence
  SuppliedParameterReference | Supplied parameter reference: this is an internal expression used to refer to the value of the n'th parameter supplied on a template call or a call to an inline function.
  SystemFunctionCall | A call to a system-defined function (specifically, a function implemented as an instance of `SystemFunction`)
  SystemFunctionCall.Optimized | Subclass representing a system function call that has been optimized; this overrides the optimize() method to do nothing, thus ensuring that optimization converges.
  TailCallLoop | A TailCallLoop wraps the body of a function that contains tail-recursive function calls.
  TailCallLoop.TailCallComponent |
  TailCallLoop.TailCallFunction |
  TailExpression | A TailExpression represents a FilterExpression of the form `EXPR[position() > n]` Here n is usually 2, but we allow other values
  TailIterator | TailIterator iterates over a base sequence starting at an element other than the first.
  TreatExpression | Treat Expression: implements "treat as data-type ( expression )".
  TryCatch | This class implements a try/catch expression.
  TryCatch.CatchClause |
  UnaryExpression | Unary Expression: an expression taking a single operand expression
  UnionCastableFunction | Function to test castability to a union type
  UnionConstructorFunction | Function to perform a cast to a union type
  UnionEnumeration | An enumeration representing a nodeset that is a union of two other NodeSets.
  UnionIterator | A multi-way union delivering the sorted results obtained from a number of sorted input iterators
  UntypedSequenceConverter | An UntypedSequenceConverter is an expression that performs a cast on each member of a supplied sequence that is an untypedAtomic value, while leaving other items unchanged
  UntypedSequenceConverter.UntypedConverter | A Converter that converts untyped atomic values to the required type, while leaving other values unchanged
  UserFunctionCall | This class represents a call to a user-defined function in the stylesheet or query.
  ValueComparison | ValueComparison: a boolean expression that compares two atomic values for equals, not-equals, greater-than or less-than.
  ValueTailIterator | `ValueTailIterator` iterates over a base sequence starting at an element other than the first.
  VariableReference | Variable reference: a reference to a variable.
  VennExpression | An expression representing a nodeset that is a union, difference, or intersection of two other NodeSets
  XPathContextMajor | This class represents a "major context" in which an XPath expression is evaluated: a "major context" object allows all aspects of the dynamic context to change, whereas a "minor context" only allows changes to the focus and the destination for push output.
  XPathContextMajor.ThreadManager | The ThreadManager is used to manage asynchronous execution of xsl:result-document instructions in Saxon-EE.
  XPathContextMinor | This class represents a minor change in the dynamic context in which an XPath expression is evaluated: a "major context" object allows all aspects of the dynamic context to change, whereas a "minor context" only allows changes to the focus and the destination for push output.
  XPathContextMinor.LastValue | Container for cached value of the last() function.

- Enum Summary
  Enum | Description
  --- | ---
  EvaluationMode | An evaluation mode represents a way in which expressions can be evaluated
  GeneralComparison.ComparisonCardinality |
  OperandUsage | The usage of an operand defines how the containing expression makes use of the value of the operand, as defined in the XSLT 3.0 specification.