Expr

java.lang.Object
- org.basex.data.ExprInfo
- - org.basex.query.expr.Expr

Direct Known Subclasses:

ParseExpr, Value
```
public abstract class Expr
extends ExprInfo
```
Abstract class for representing XQuery expressions. Expression are divided into ParseExpr and Value classes.

Author:

BaseX Team 2005-12, BSD License, Christian Gruen

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class Expr.Use
Flags that influence query compilation.

Nested Classes
Modifier and Type	Class and Description
`static class`	`Expr.Use` Flags that influence query compilation.

Constructor Summary

Constructors
Constructor and Description

Expr()

Constructors
Constructor and Description
`Expr()`

Method Summary

Methods
Modifier and Type	Method and Description
`Expr`	`addText(QueryContext ctx)` Optionally adds a text node to an expression for potential index rewriting.
`abstract Expr`	`comp(QueryContext ctx)` Compiles and optimizes the expression, assigns data types and cardinalities.
`Expr`	`compEbv(QueryContext ctx)` This method is called at compile time by expressions that perform effective boolean value tests (e.g.
`abstract int`	`count(Var v)` Counts how often the specified variable is used by an expression.
`abstract Item`	`ebv(QueryContext ctx, InputInfo ii)` Checks if the iterator can be dissolved into an effective boolean value.
`boolean`	`hasFreeVars(QueryContext ctx)` Checks if this expression has free variables.
`boolean`	`indexAccessible(IndexContext ic)` Checks if an expression can be rewritten to an index access.
`Expr`	`indexEquivalent(IndexContext ic)` Returns an equivalent expression which accesses an index structure.
`boolean`	`isEmpty()` Tests if this is an empty sequence.
`boolean`	`isFunction(Function f)` Checks if this expression is a certain function.
`boolean`	`isItem()` Tests if this is an item.
`boolean`	`isVacuous()` Tests if this is a vacuous expression (empty sequence or error function).
`boolean`	`isValue()` Tests if this is a value.
`abstract Item`	`item(QueryContext ctx, InputInfo ii)` Evaluates the expression and returns the resulting item or a `null` reference, if the expression yields an empty sequence.
`abstract Iter`	`iter(QueryContext ctx)` Evaluates the expression and returns an iterator on the resulting items.
`boolean`	`iterable()` Returns true if the expression is iterable, i.e., if it does not contain any duplicates and if all results are sorted.
`Expr`	`markTailCalls()` Finds and marks tail calls, enabling TCO.
`abstract boolean`	`removable(Var v)` Checks if the specified variable is replaceable by a context item.
`abstract Expr`	`remove(Var v)` Substitutes all `VarRef` expressions for the given variable by a `Context` reference.
`boolean`	`sameAs(Expr cmp)` Compares the current and specified expression for equality.
`abstract long`	`size()` Returns the sequence size or 1.
`abstract Item`	`test(QueryContext ctx, InputInfo ii)` Performs a predicate test and returns the item if test was successful.
`abstract SeqType`	`type()` Returns the sequence type of the evaluated value.
`abstract boolean`	`uses(Expr.Use u)` Indicates if an expression uses the specified type or operation.
`abstract Value`	`value(QueryContext ctx)` Evaluates the expression and returns the resulting value.

Methods inherited from class org.basex.data.ExprInfo
description, info, plan, toString

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

- Constructor Detail
  - Expr
```
public Expr()
```
- Method Detail
  - comp
```
public abstract Expr comp(QueryContext ctx)
                   throws QueryException
```
    Compiles and optimizes the expression, assigns data types and cardinalities.
    
    Parameters:
    ctx - query context
    
    Returns:
    optimized expression
    
    Throws:
    
    QueryException - query exception
  - iter
```
public abstract Iter iter(QueryContext ctx)
                   throws QueryException
```
    Evaluates the expression and returns an iterator on the resulting items. If this method is not overwritten, item(org.basex.query.QueryContext, org.basex.util.InputInfo) must be implemented by an expression, as it may be called by this method.
    
    Parameters:
    ctx - query context
    
    Returns:
    resulting item
    
    Throws:
    
    QueryException - query exception
  - item
```
public abstract Item item(QueryContext ctx,
        InputInfo ii)
                   throws QueryException
```
    Evaluates the expression and returns the resulting item or a null reference, if the expression yields an empty sequence. If this method is not overwritten, iter(org.basex.query.QueryContext) must be implemented by an expression, as it may be called by this method.
    
    Parameters:
    ctx - query context
    ii - input info
    
    Returns:
    iterator
    
    Throws:
    
    QueryException - query exception
  - value
```
public abstract Value value(QueryContext ctx)
                     throws QueryException
```
    Evaluates the expression and returns the resulting value.
    
    Parameters:
    ctx - query context
    
    Returns:
    iterator
    
    Throws:
    
    QueryException - query exception
  - ebv
```
public abstract Item ebv(QueryContext ctx,
       InputInfo ii)
                  throws QueryException
```
    Checks if the iterator can be dissolved into an effective boolean value. If not, returns an error. If yes, returns the first value - which can be also be e.g. an integer, which is later evaluated as numeric predicate.
    
    Parameters:
    ctx - query context
    ii - input info
    
    Returns:
    item
    
    Throws:
    
    QueryException - query exception
  - test
```
public abstract Item test(QueryContext ctx,
        InputInfo ii)
                   throws QueryException
```
    Performs a predicate test and returns the item if test was successful.
    
    Parameters:
    ctx - query context
    ii - input info
    
    Returns:
    item
    
    Throws:
    
    QueryException - query exception
  - isEmpty
```
public boolean isEmpty()
```
    Tests if this is an empty sequence. This function is only overwritten by the Empty class, which represents the empty sequence.
    
    Returns:
    result of check
  - isVacuous
```
public boolean isVacuous()
```
    Tests if this is a vacuous expression (empty sequence or error function). This check is needed for updating queries.
    
    Returns:
    result of check
  - isValue
```
public boolean isValue()
```
    Tests if this is a value.
    
    Returns:
    result of check
  - isItem
```
public boolean isItem()
```
    Tests if this is an item.
    
    Returns:
    result of check
  - size
```
public abstract long size()
```
    Returns the sequence size or 1.
    
    Returns:
    result of check
  - uses
```
public abstract boolean uses(Expr.Use u)
```
    Indicates if an expression uses the specified type or operation. This method is called by numerous comp(org.basex.query.QueryContext) methods to test the properties of sub-expressions. It will return true as soon as at least one test is successful.
    
    Parameters:
    u - type/operation to be found
    
    Returns:
    result of check
  - count
```
public abstract int count(Var v)
```
    Counts how often the specified variable is used by an expression. This method is called by:
    - GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses as predicates and remove statically bound or unused clauses
    - GFLWOR.compHoist(org.basex.query.QueryContext) to hoist independent variables
    Parameters:
    v - variable to be checked
    
    Returns:
    number of occurrences
  - removable
```
public abstract boolean removable(Var v)
```
    Checks if the specified variable is replaceable by a context item. The following tests might return false:
    - Preds.removable(org.basex.query.util.Var), if one of the variables is used within a predicate.
    - MixedPath.removable(org.basex.query.util.Var), if the variable occurs within the path.
    - Group.removable(org.basex.query.util.Var), as the group by expression depends on variable references.
    This method is called by GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses into predicates.
    Parameters:
    v - variable to be replaced
    
    Returns:
    result of check
  - remove
```
public abstract Expr remove(Var v)
```
    Substitutes all VarRef expressions for the given variable by a Context reference. This method is called by GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses as predicates.
    
    Parameters:
    v - variable to be replaced
    
    Returns:
    new expression
  - compEbv
```
public Expr compEbv(QueryContext ctx)
```
    This method is called at compile time by expressions that perform effective boolean value tests (e.g. If or Preds). If the arguments of the called expression return a boolean anyway, the expression will be simplified.
    
    Example in CmpV: if($x eq true()) is rewritten to if($x), if $x will always yield a single boolean.
    
    Parameters:
    ctx - query context
    
    Returns:
    optimized expression
  - type
```
public abstract SeqType type()
```
    Returns the sequence type of the evaluated value. For simplicity, some types have been summarized. E.g., all numbers are treated as integers.
    
    Returns:
    result of check
  - iterable
```
public boolean iterable()
```
    Returns true if the expression is iterable, i.e., if it does not contain any duplicates and if all results are sorted. This method is called e.g. by AxisPath.
    
    Returns:
    result of check
  - indexAccessible
```
public boolean indexAccessible(IndexContext ic)
                        throws QueryException
```
    Checks if an expression can be rewritten to an index access. If this method is implemented, indexEquivalent(org.basex.query.util.IndexContext) must be implemented as well.
    
    Parameters:
    ic - index context
    
    Returns:
    true if an index can be used
    
    Throws:
    
    QueryException - query exception
  - indexEquivalent
```
public Expr indexEquivalent(IndexContext ic)
                     throws QueryException
```
    Returns an equivalent expression which accesses an index structure. Will be called if indexAccessible(org.basex.query.util.IndexContext) is returns true for an expression.
    
    Parameters:
    ic - index context
    
    Returns:
    equivalent index-expression
    
    Throws:
    
    QueryException - query exception
  - sameAs
```
public boolean sameAs(Expr cmp)
```
    Compares the current and specified expression for equality.
    
    Parameters:
    cmp - expression to be compared
    
    Returns:
    result of check
  - isFunction
```
public boolean isFunction(Function f)
```
    Checks if this expression is a certain function.
    
    Parameters:
    f - function definition
    
    Returns:
    result of check
  - addText
```
public Expr addText(QueryContext ctx)
```
    Optionally adds a text node to an expression for potential index rewriting.
    
    Parameters:
    ctx - query context
    
    Returns:
    expression
  - hasFreeVars
```
public boolean hasFreeVars(QueryContext ctx)
```
    Checks if this expression has free variables.
    
    Parameters:
    ctx - query context on the level of this expression
    
    Returns:
    true if there are variables which are used but not declared in this expression, false otherwise
  - markTailCalls
```
public Expr markTailCalls()
```
    Finds and marks tail calls, enabling TCO.
    
    Returns:
    the expression, with tail calls marked

Class Expr

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class org.basex.data.ExprInfo

Methods inherited from class java.lang.Object

Constructor Detail

Expr

Method Detail

comp

iter

item

value

ebv

test

isEmpty

isVacuous

isValue

isItem

size

uses

count

removable

remove

compEbv

type

iterable

indexAccessible

indexEquivalent

sameAs

isFunction

addText

hasFreeVars

markTailCalls