Package org.projog.core.parser

Class Operands

java.lang.Object

org.projog.core.parser.Operands

public final class Operands
extends java.lang.Object

Collection of operands.

Prolog allows functors (names of predicates) to be defined as "operators". The use of operators allows syntax to be easier to read.

Infix operators are placed between their two arguments. Prefix operators are placed before their single argument. Postfix operators are placed after their single argument.

A common use of operators is in the definition of arithmetic operations. By declaring is and - as infix operators we can write valid prolog syntax like X is 1 + 2. instead of is(X, +(1, 2)).

Each KnowledgeBase has a single unique Operands instance.

See Also:

KnowledgeBase.getOperands()

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static class	Operands.Associativity	Associativity is used to specify rules over operators in the same expression that have the same priority.
private static class	Operands.Location
private static class	Operands.Operand

Field Summary

Fields

Modifier and Type	Field	Description
private java.util.Map<java.lang.String,Operands.Operand>	infixOperands
private java.lang.Object	LOCK
private java.util.Map<java.lang.String,Operands.Operand>	postfixOperands
private java.util.Map<java.lang.String,Operands.Operand>	prefixOperands

Constructor Summary

Constructors

Constructor	Description
Operands()

Method Summary

Modifier and Type	Method	Description
void	addOperand(java.lang.String operandName, java.lang.String associativityName, int precedence)	Adds a new operator.
boolean	fx(java.lang.String op)	Returns true if op represents a prefix operator with associativity of fx, else false.
boolean	fy(java.lang.String op)	Returns true if op represents a prefix operator with associativity of fy, else false.
private Operands.Associativity	getAssociativity(java.lang.String associativityName)
int	getInfixPriority(java.lang.String op)	Returns the priority (precedence/level) of the infix operator represented by op.
private java.util.Map<java.lang.String,Operands.Operand>	getOperandsMap(Operands.Associativity a)
int	getPostfixPriority(java.lang.String op)	Returns the priority (precedence/level) of the postfix operator represented by op.
int	getPrefixPriority(java.lang.String op)	Returns the priority (precedence/level) of the prefix operator represented by op.
boolean	infix(java.lang.String op)	Returns true if op represents an infix operator, else false.
boolean	isDefined(java.lang.String commandName)	Returns true if commandName represents any known operator, else false.
boolean	postfix(java.lang.String op)	Returns true if op represents a postfix operator, else false.
boolean	prefix(java.lang.String op)	Returns true if op represents a prefix operator, else false.
boolean	xf(java.lang.String op)	Returns true if op represents a postfix operator with associativity of xf, else false.
boolean	xfx(java.lang.String op)	Returns true if op represents an infix operator with associativity of xfx, else false.
boolean	xfy(java.lang.String op)	Returns true if op represents an infix operator with associativity of xfy, else false.
boolean	yf(java.lang.String op)	Returns true if op represents a postfix operator with associativity of yf, else false.
boolean	yfx(java.lang.String op)	Returns true if op represents an infix operator with associativity of yfx, else false.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

LOCK

private final java.lang.Object LOCK

infixOperands

private final java.util.Map<java.lang.String,Operands.Operand> infixOperands

prefixOperands

private final java.util.Map<java.lang.String,Operands.Operand> prefixOperands

postfixOperands

private final java.util.Map<java.lang.String,Operands.Operand> postfixOperands

Constructor Detail

Operands

public Operands()

Method Detail

addOperand

public void addOperand(java.lang.String operandName,
                       java.lang.String associativityName,
                       int precedence)

Adds a new operator.

Parameters:

operandName - the name of the new operator

associativityName - the operators associativity (must be one of: xfx, xfy, yfx, fx, fy, xf or yf)

precedence - used to specify the ordering of terms where it is not made explicit by the use of brackets

getAssociativity

private Operands.Associativity getAssociativity(java.lang.String associativityName)

getOperandsMap

private java.util.Map<java.lang.String,Operands.Operand> getOperandsMap(Operands.Associativity a)

getInfixPriority

public int getInfixPriority(java.lang.String op)

Returns the priority (precedence/level) of the infix operator represented by op.

getPrefixPriority

public int getPrefixPriority(java.lang.String op)

Returns the priority (precedence/level) of the prefix operator represented by op.

getPostfixPriority

public int getPostfixPriority(java.lang.String op)

Returns the priority (precedence/level) of the postfix operator represented by op.

infix

public boolean infix(java.lang.String op)

Returns true if op represents an infix operator, else false.

yfx

public boolean yfx(java.lang.String op)

Returns true if op represents an infix operator with associativity of yfx, else false.

xfy

public boolean xfy(java.lang.String op)

Returns true if op represents an infix operator with associativity of xfy, else false.

xfx

public boolean xfx(java.lang.String op)

Returns true if op represents an infix operator with associativity of xfx, else false.

prefix

public boolean prefix(java.lang.String op)

Returns true if op represents a prefix operator, else false.

fx

public boolean fx(java.lang.String op)

Returns true if op represents a prefix operator with associativity of fx, else false.

fy

public boolean fy(java.lang.String op)

Returns true if op represents a prefix operator with associativity of fy, else false.

postfix

public boolean postfix(java.lang.String op)

Returns true if op represents a postfix operator, else false.

xf

public boolean xf(java.lang.String op)

Returns true if op represents a postfix operator with associativity of xf, else false.

yf

public boolean yf(java.lang.String op)

Returns true if op represents a postfix operator with associativity of yf, else false.

isDefined

public boolean isDefined(java.lang.String commandName)

Returns true if commandName represents any known operator, else false.