jminusminus

Class LookaheadScanner

java.lang.Object

jminusminus.LookaheadScanner

 class LookaheadScanner
extends Object

A lexical analyzer for j-- that interfaces with the hand-written parser (Parser.java). It provides a backtracking mechanism, and makes use of the underlying hand-written Scanner.

Field Summary

Fields

Modifier and Type	Field and Description
boolean	isLookingAhead Whether we are looking ahead.

Constructor Summary

Constructors

Constructor and Description
LookaheadScanner(String fileName) Construct a LookaheadScanner from a file name.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	errorHasOccured() Has an error occurred up to now in lexical analysis?
String	fileName() Return the name of the source file.
void	next() Scan to the next token in the input.
TokenInfo	previousToken() The previously scanned token.
void	recordPosition() Record the current position in the input, so that we can start looking ahead in the input (and later return to this position).
void	returnToPosition() Return to the previously recorded position in the input stream of tokens.
TokenInfo	token() The currently scanned token.

Methods inherited from class java.lang.Object

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

Field Detail

isLookingAhead

public boolean isLookingAhead

Whether we are looking ahead.

Constructor Detail

LookaheadScanner

public LookaheadScanner(String fileName)
                 throws FileNotFoundException

Construct a LookaheadScanner from a file name.

Parameters:

fileName - the name of the file containing the source.

Throws:

FileNotFoundException - when the named file cannot be found.

Method Detail

next

public void next()

Scan to the next token in the input.

recordPosition

public void recordPosition()

Record the current position in the input, so that we can start looking ahead in the input (and later return to this position). We'll queue up the current and subsequent tokens until returnToPosition() is invoked. These recordPosition's can be nested.

returnToPosition

public void returnToPosition()

Return to the previously recorded position in the input stream of tokens. If this is a nested lookahead, then return to the previous token queue.

token

public TokenInfo token()

The currently scanned token.

Returns:

the current token.

previousToken

public TokenInfo previousToken()

The previously scanned token. We use this in the parser to get at a token's semantic info (for example an identifier's name), after we've scanned it.

Returns:

the previous token.

errorHasOccured

public boolean errorHasOccured()

Has an error occurred up to now in lexical analysis?

Returns:

true or false.

fileName

public String fileName()

Return the name of the source file.

Returns:

name of the source file.