uk.ac.sheffield.vtts.model

Class Projection

java.lang.Object

uk.ac.sheffield.vtts.model.Element

uk.ac.sheffield.vtts.model.Named

uk.ac.sheffield.vtts.model.Expression

uk.ac.sheffield.vtts.model.Function

uk.ac.sheffield.vtts.model.Projection

public class Projection
extends Function

Projection represents a function creating, or projecting from, a tuple. There are three projection operators, whose names are: pair, first and second. The only supported tuple-kind is a pair of values, having the model type Pair[K, V] for some types K and V. Pairs are used as maplets in Map types.

Version:

Broker@Cloud 1.0

Author:

Anthony J H Simons

Field Summary

Fields inherited from class uk.ac.sheffield.vtts.model.Function

expressions, maxOperands

Fields inherited from class uk.ac.sheffield.vtts.model.Expression

factory, type

Fields inherited from class uk.ac.sheffield.vtts.model.Named

name

Constructor Summary

Constructors

Constructor and Description
Projection() Creates a default Projection.
Projection(java.lang.String name) Creates a Projection with the given operator name.
Projection(java.lang.String name, java.lang.String type) Creates a Projection with the given operator name and result type.

Method Summary

Methods

Modifier and Type	Method and Description
java.lang.Object	evaluate() Evaluates this Projection expression.
protected java.lang.Object	first(java.lang.Object pair) Returns the first projection from an ordered pair.
java.lang.String	getType() Returns the result type of this Projection.
protected void	nameCheck() Checks the name of this Projection expression and sets the number of operands to one for a projection and two for a pair construction.
protected java.util.Map.Entry<java.lang.Object,java.lang.Object>	pair(java.lang.Object first, java.lang.Object second) Returns a new ordered pair, consisting of the first and second objects.
void	rebind(java.lang.Object result) Rebinds the unbound parameters in this Projection expression, so that it yields the given expected result.
protected java.lang.Object	second(java.lang.Object pair) Returns the second projection from an ordered pair.
protected void	typeCheck() Checks that the types of the operands and result are consistent.

Methods inherited from class uk.ac.sheffield.vtts.model.Function

addExpression, assign, equals, getExpressions, hashCode, isAssignable, isBound, operand, rebind, resolve, setName, toString, unbind

Methods inherited from class uk.ac.sheffield.vtts.model.Expression

getName, isBottom, isOrdered, setType

Methods inherited from class uk.ac.sheffield.vtts.model.Named

setName

Methods inherited from class uk.ac.sheffield.vtts.model.Element

safeEquals, safeHashCode, semanticError

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

Projection

public Projection()

Creates a default Projection.

Projection

public Projection(java.lang.String name)

Creates a Projection with the given operator name.

Parameters:

name - the projection operator name.

Projection

public Projection(java.lang.String name,
          java.lang.String type)

Creates a Projection with the given operator name and result type.

Parameters:

name - the projection operator name.

type - the result type of this operator.

Method Detail

nameCheck

protected void nameCheck()
                  throws SemanticError

Checks the name of this Projection expression and sets the number of operands to one for a projection and two for a pair construction.

Specified by:

nameCheck in class Function

Throws:

SemanticError - if the name is illegal.

typeCheck

protected void typeCheck()
                  throws SemanticError

Checks that the types of the operands and result are consistent. If the operator is "pair", checks that the result is of a pair-type and the arguments of the corresponding key-type and value-type. Otherwise checks that the argument is of a pair-type, and that the projections are of the corresponding key-type and value-type. Caches the pairType, keyType and valueType for use during binding and value synthesis.

Specified by:

typeCheck in class Function

Throws:

SemanticError - if a type inconsistency is detected.

getType

public java.lang.String getType()

Returns the result type of this Projection. Returns the explicitly given type, otherwise infers this type by a heuristic. If the operator is "pair", infers the pair-type from the types of the two operands. Otherwise, infers the "first" or "second" projection type from the type of the sole operand. Caches the inferred type.

Overrides:

getType in class Function

Returns:

the type of this Projection.

Throws:

SemanticError - if no type can be inferred.

evaluate

public java.lang.Object evaluate()

Evaluates this Projection expression. Dispatches internally on the name of the operator to one of the pair-operations.

Specified by:

evaluate in class Expression

Returns:

the Java object denoting the value of this Expression.

pair

protected java.util.Map.Entry<java.lang.Object,java.lang.Object> pair(java.lang.Object first,
                                                          java.lang.Object second)

Returns a new ordered pair, consisting of the first and second objects.

Parameters:

first - the first projection.

second - the second projection.

Returns:

the pair containing the first and second projections.

first

protected java.lang.Object first(java.lang.Object pair)

Returns the first projection from an ordered pair.

Parameters:

pair - the ordered pair.

Returns:

the first projection, the object ordered first.

second

protected java.lang.Object second(java.lang.Object pair)

Returns the second projection from an ordered pair.

Parameters:

pair - the ordered pair.

Returns:

the second projection, the object ordered second.

rebind

public void rebind(java.lang.Object result)

Rebinds the unbound parameters in this Projection expression, so that it yields the given expected result.

Specified by:

rebind in class Expression

Parameters:

result - the desired bound value.