slogo.parser

Class ExpressionParser

java.lang.Object

slogo.parser.ExpressionParser

All Implemented Interfaces:

Parser

public class ExpressionParser
extends java.lang.Object
implements Parser

This is a recursive descent parser for parsing expressions using the standard grammar for expressions (follows).

 expression ::= term
            ::= term + expression
            ::= term - expression
 term       ::= factor
            ::= factor * term
            ::= factor / term
 factor     ::= number
            ::= - factor
            ::= ( expression )
 

This class has undergone basic though not thorough testing

Field Summary

Fields

Modifier and Type	Field and Description
private SLogoParser	myParser
private static ExpressionParser	ourInstance

Constructor Summary

Constructors

Modifier	Constructor and Description
private	ExpressionParser() Parse expressions from a parser

Method Summary

Methods

Modifier and Type	Method and Description
static ExpressionParser	getInstance()
private boolean	isAddOrSubtractToken(Token t)
private boolean	isMultOrDivToken(Token t)
GrammarElement	parse(SLogoParser ep) parses the expression with the given parser
protected Expression	parseExpression()
protected Expression	parseFactor()
protected Expression	parseTerm()

Methods inherited from class java.lang.Object

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

Field Detail

ourInstance

private static ExpressionParser ourInstance

myParser

private SLogoParser myParser

Constructor Detail

ExpressionParser

private ExpressionParser()

Parse expressions from a parser

Method Detail

getInstance

public static ExpressionParser getInstance()

Returns:

the one instance of this class

parse

public GrammarElement parse(SLogoParser ep)

parses the expression with the given parser

Specified by:

parse in interface Parser

isAddOrSubtractToken

private boolean isAddOrSubtractToken(Token t)

Parameters:

t - the token being compared

Returns:

true iff this is an addition or substraction token

isMultOrDivToken

private boolean isMultOrDivToken(Token t)

Parameters:

t - token being compared

Returns:

true iff this is a multiplication or division token

parseExpression

protected Expression parseExpression()

Returns:

the expression generated from parsing the tokens.

parseTerm

protected Expression parseTerm()

Returns:

the expression generated from parsing the term

parseFactor

protected Expression parseFactor()

Returns:

the expression generated from parsing the factor