uk.ac.sheffield.vtts.model

Class Function

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

Direct Known Subclasses:

Arithmetic, Assignment, Manipulation, Predicate, Projection

public abstract class Function
extends Expression

Function represents a functional expression with a function root node. A Function represents any kind of executable expression that is dominated by a principal operator that acts on zero or more operands. Subclasses of Function cater to different kinds of operation. The name of a Function is validated, and may be used to constrain the legal number of operands.

Version:

Broker@Cloud 1.0

Author:

Anthony J H Simons

Field Summary

Fields

Modifier and Type	Field and Description
protected java.util.List<Expression>	expressions The operands of this function.
protected int	maxOperands The maximum number of operands, initially inactive when set to -1.

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
Function() Creates a default functional expression.
Function(java.lang.String name) Creates a named functional expression.
Function(java.lang.String name, java.lang.String type) Creates a named and typed functional expression.

Method Summary

Methods

Modifier and Type	Method and Description
Function	addExpression(Expression expression) Adds an expression as an operand to this functional expression.
void	assign(java.lang.Object value) Reports an attempt to assign to this Function as an error.
boolean	equals(java.lang.Object other) Reports whether this function is equal to another object.
java.util.List<Expression>	getExpressions() Returns a list of the operand expressions governed by this functional expression.
java.lang.String	getType() Returns the result type of this Function.
int	hashCode() Returns a quasi-unique hash code for this function.
boolean	isAssignable() Reports whether this Function is re-assignable.
boolean	isBound() Reports whether this Function expression is bound.
protected abstract void	nameCheck() Checks the chosen name for this Function and sets the maximum number of operands.
Expression	operand(int index) Returns the given operand Expression at an index.
void	rebind() Rebinds the unbound operands of this Function.
Function	resolve(Scope scope) Causes this Function to resolve its global/local Parameter references.
Function	setName(java.lang.String name) Sets the name of this Function.
java.lang.String	toString() Converts this function to a printable string.
protected abstract void	typeCheck() Checks that the operand types and result type are consistent, for this kind of Function.
void	unbind() Unbinds the operands of this Function.

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

evaluate, getName, isBottom, isOrdered, rebind, 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

Field Detail

maxOperands

protected int maxOperands

The maximum number of operands, initially inactive when set to -1.

expressions

protected java.util.List<Expression> expressions

The operands of this function.

Constructor Detail

Function

public Function()

Creates a default functional expression.

Function

public Function(java.lang.String name)

Creates a named functional expression.

Parameters:

name - the name of the function.

Function

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

Creates a named and typed functional expression.

Parameters:

name - the name of this functional expression.

type - the type of this functional expression.

Method Detail

nameCheck

protected abstract void nameCheck()
                           throws SemanticError

Checks the chosen name for this Function and sets the maximum number of operands. This is overridden in each subclass, according to the kind of Function.

Throws:

SemanticError - if the name is illegal.

typeCheck

protected abstract void typeCheck()
                           throws SemanticError

Checks that the operand types and result type are consistent, for this kind of Function.

Throws:

SemanticError - if a type inconsistency is detected.

equals

public boolean equals(java.lang.Object other)

Reports whether this function is equal to another object. True if the other object is a function with the same name, type and operands as this; otherwise false.

Overrides:

equals in class Expression

Parameters:

other - the other object.

Returns:

true if both functions have the same name, type and operands.

hashCode

public int hashCode()

Returns a quasi-unique hash code for this function. The hash code is computed from the hash codes for the meta-type, name, type and operand expressions.

Overrides:

hashCode in class Expression

Returns:

the hash code for this expression.

setName

public Function setName(java.lang.String name)

Sets the name of this Function. Validates the name.

Overrides:

setName in class Named

Parameters:

name - the name to set.

Returns:

this Named element.

getType

public java.lang.String getType()

Returns the result type of this Function. Returns the explicitly given type, otherwise infers this type by a heuristic. The default heuristic returns the type of the first operand, which works for most cases. Caches the retrieved type as the type of this Function.

Overrides:

getType in class Expression

Returns:

the type of this Function.

Throws:

SemanticError - if no type can be inferred.

isAssignable

public boolean isAssignable()

Reports whether this Function is re-assignable. Returns the result false, since a Function may not be modified by an Assignment.

Specified by:

isAssignable in class Expression

Returns:

false.

addExpression

public Function addExpression(Expression expression)
                       throws SemanticError

Adds an expression as an operand to this functional expression.

Parameters:

expression - the operand expression.

Returns:

this functional expression.

Throws:

SemanticError

getExpressions

public java.util.List<Expression> getExpressions()

Returns a list of the operand expressions governed by this functional expression.

Returns:

a list of this functional expression's expressions.

operand

public Expression operand(int index)

Returns the given operand Expression at an index.

Parameters:

index - the index.

Returns:

the operand Expression.

assign

public void assign(java.lang.Object value)

Reports an attempt to assign to this Function as an error.

Specified by:

assign in class Expression

Parameters:

value - the value to assign.

isBound

public boolean isBound()

Reports whether this Function expression is bound.

Specified by:

isBound in class Expression

Returns:

true if every sub-expression is bound.

unbind

public void unbind()

Unbinds the operands of this Function. Propagates the request to each operand Expression. Non-constant Parameters will release their bound values, and Functions will forward the request, recursively.

Specified by:

unbind in class Expression

rebind

public void rebind()

Rebinds the unbound operands of this Function. Propagates the request to each operand Expression. Non-constant Parameters will be reset to their default values, and Functions will forward the request, recursively.

Specified by:

rebind in class Expression

resolve

public Function resolve(Scope scope)

Causes this Function to resolve its global/local Parameter references. The Expressions that are this Function's operands may contain arbitrary Functions or Parameters. All Parameter references must be resolved to declared Parameters in global Memory scope, or local Operation scope. This method ensures that all Parameter references actually correspond to some declared Parameter. Substitutes all duplicate copies of such Parameters by a reference to the original copy.

Specified by:

resolve in class Expression

Parameters:

scope - a table of global and local Parameters.

Returns:

this Expression.

toString

public java.lang.String toString()

Converts this function to a printable string. The output is a string of the form: function(node1, node2) giving the name of the function and the recursive print-forms of the operands.

Overrides:

toString in class Named

Returns:

the String representation of this Named element.