slogo.parser
Class SLogoParser

java.lang.Object
  slogo.parser.SLogoParser

public class SLogoParser
extends java.lang.Object

Illustrates the java.io.StreamTokenizer class and how it can be used to parse tokens for a toy example programming language (elan). For this example simple instructions are parsed, but lots of infrastructure is in place for parsing a more complete language.

Author:

Owen Astrachan

See Also:

slogo.expression, slogo.instruction, InstructionParser

Field Summary

protected SLogoContext	myContext
java.lang.Object	myResult
protected Token	myToken
protected java.io.StreamTokenizer	myTokenizer

Constructor Summary

SLogoParser(Turtle turtle)

Method Summary

void	error(Token t)
Context	getContext()
java.lang.Object	getMyResult()
Token	getToken() returns the current token, doesn't fetch a new one
java.lang.Object	interpret(java.io.Reader r) parses an expression and prints the result of evaluating the expression.
java.lang.Object	interpret(java.lang.String cmd)
static void	main(java.lang.String[] args) Basic driver for SLogoParser
Token	match(Token rhs) try to match a token, if unsuccessful throw an exception, otherwise match succeeds, and next token is obtained and returned
protected Token	nextToken() get the next token and store it for retrieval by getToken()
protected GrammarElement	parseInstructionParameter()
protected java.util.List<GrammarElement>	parseInstructionParameters(int numParameters)

Methods inherited from class java.lang.Object

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

Field Detail

myTokenizer

protected java.io.StreamTokenizer myTokenizer

myToken

protected Token myToken

myContext

protected SLogoContext myContext

myResult

public java.lang.Object myResult

Constructor Detail

SLogoParser

public SLogoParser(Turtle turtle)

Method Detail

interpret

public java.lang.Object interpret(java.lang.String cmd)

Parameters:

cmd - string command from text field

interpret

public java.lang.Object interpret(java.io.Reader r)

parses an expression and prints the result of evaluating the expression.

Parameters:

r - the reader that will be tokenized

Returns:

the result of executing the last command

nextToken

protected Token nextToken()

get the next token and store it for retrieval by getToken()

Returns:

the current (just read) token

getToken

public Token getToken()

returns the current token, doesn't fetch a new one

Returns:

the current token

parseInstructionParameter

protected GrammarElement parseInstructionParameter()

Returns:

parseInstructionParameters

protected java.util.List<GrammarElement> parseInstructionParameters(int numParameters)

Parameters:

numParameters -

Returns:

match

public Token match(Token rhs)

try to match a token, if unsuccessful throw an exception, otherwise match succeeds, and next token is obtained and returned

Parameters:

rhs - token being matched

Returns:

the next read token

Throws:

ParseException - if match fails

error

public void error(Token t)

Parameters:

t - token where error occurred

Throws:

a - ParseException labeled by t

getContext

public Context getContext()

getMyResult

public java.lang.Object getMyResult()

main

public static void main(java.lang.String[] args)

Basic driver for SLogoParser

Parameters:

args -