org.antlr.runtime.Lexer Maven / Gradle / Ivy
/*
[The "BSD licence"]
Copyright (c) 2005-2006 Terence Parr
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package org.antlr.runtime;
/** A lexer is recognizer that draws input symbols from a character stream.
* lexer grammars result in a subclass of this object. A Lexer object
* uses simplified match() and error recovery mechanisms in the interest
* of speed.
*/
public abstract class Lexer extends BaseRecognizer implements TokenSource {
/** Where is the lexer drawing characters from? */
protected CharStream input;
/** The goal of all lexer rules/methods is to create a token object.
* This is an instance variable as multiple rules may collaborate to
* create a single token. nextToken will return this object after
* matching lexer rule(s). If you subclass to allow multiple token
* emissions, then set this to the last token to be matched or
* something nonnull so that the auto token emit mechanism will not
* emit another token.
*/
protected Token token;
/** What character index in the stream did the current token start at?
* Needed, for example, to get the text for current token. Set at
* the start of nextToken.
*/
protected int tokenStartCharIndex = -1;
/** The line on which the first character of the token resides */
protected int tokenStartLine;
/** The character position of first character within the line */
protected int tokenStartCharPositionInLine;
/** The channel number for the current token */
protected int channel;
/** The token type for the current token */
protected int type;
/** You can set the text for the current token to override what is in
* the input char buffer. Use setText() or can set this instance var.
*/
protected String text;
public Lexer() {
}
public Lexer(CharStream input) {
this.input = input;
}
public void reset() {
super.reset(); // reset all recognizer state variables
// wack Lexer state variables
token = null;
type = Token.INVALID_TOKEN_TYPE;
channel = Token.DEFAULT_CHANNEL;
tokenStartCharIndex = -1;
tokenStartCharPositionInLine = -1;
tokenStartLine = -1;
text = null;
if ( input!=null ) {
input.seek(0); // rewind the input
}
}
/** Return a token from this source; i.e., match a token on the char
* stream.
*/
public Token nextToken() {
while (true) {
token = null;
channel = Token.DEFAULT_CHANNEL;
tokenStartCharIndex = input.index();
tokenStartCharPositionInLine = input.getCharPositionInLine();
tokenStartLine = input.getLine();
text = null;
if ( input.LA(1)==CharStream.EOF ) {
return Token.EOF_TOKEN;
}
try {
mTokens();
if ( token==null ) {
emit();
}
else if ( token==Token.SKIP_TOKEN ) {
continue;
}
return token;
}
catch (RecognitionException re) {
reportError(re);
recover(re);
}
}
}
/** Instruct the lexer to skip creating a token for current lexer rule
* and look for another token. nextToken() knows to keep looking when
* a lexer rule finishes with token set to SKIP_TOKEN. Recall that
* if token==null at end of any token rule, it creates one for you
* and emits it.
*/
public void skip() {
token = Token.SKIP_TOKEN;
}
/** This is the lexer entry point that sets instance var 'token' */
public abstract void mTokens() throws RecognitionException;
/** Set the char stream and reset the lexer */
public void setCharStream(CharStream input) {
this.input = null;
reset();
this.input = input;
}
/** Currently does not support multiple emits per nextToken invocation
* for efficiency reasons. Subclass and override this method and
* nextToken (to push tokens into a list and pull from that list rather
* than a single variable as this implementation does).
*/
public void emit(Token token) {
this.token = token;
}
/** The standard method called to automatically emit a token at the
* outermost lexical rule. The token object should point into the
* char buffer start..stop. If there is a text override in 'text',
* use that to set the token's text. Override this method to emit
* custom Token objects.
*/
public Token emit() {
Token t = new CommonToken(input, type, channel, tokenStartCharIndex, getCharIndex()-1);
t.setLine(tokenStartLine);
t.setText(text);
t.setCharPositionInLine(tokenStartCharPositionInLine);
emit(t);
return t;
}
public void match(String s) throws MismatchedTokenException {
int i = 0;
while ( i0 ) {
failed = true;
return;
}
MismatchedTokenException mte =
new MismatchedTokenException(s.charAt(i), input);
recover(mte);
throw mte;
}
i++;
input.consume();
failed = false;
}
}
public void matchAny() {
input.consume();
}
public void match(int c) throws MismatchedTokenException {
if ( input.LA(1)!=c ) {
if ( backtracking>0 ) {
failed = true;
return;
}
MismatchedTokenException mte =
new MismatchedTokenException(c, input);
recover(mte);
throw mte;
}
input.consume();
failed = false;
}
public void matchRange(int a, int b)
throws MismatchedRangeException
{
if ( input.LA(1)b ) {
if ( backtracking>0 ) {
failed = true;
return;
}
MismatchedRangeException mre =
new MismatchedRangeException(a,b,input);
recover(mre);
throw mre;
}
input.consume();
failed = false;
}
public int getLine() {
return input.getLine();
}
public int getCharPositionInLine() {
return input.getCharPositionInLine();
}
/** What is the index of the current character of lookahead? */
public int getCharIndex() {
return input.index();
}
/** Return the text matched so far for the current token or any
* text override.
*/
public String getText() {
if ( text!=null ) {
return text;
}
return input.substring(tokenStartCharIndex,getCharIndex()-1);
}
/** Set the complete text of this token; it wipes any previous
* changes to the text.
*/
public void setText(String text) {
this.text = text;
}
public void reportError(RecognitionException e) {
/** TODO: not thought about recovery in lexer yet.
*
// if we've already reported an error and have not matched a token
// yet successfully, don't report any errors.
if ( errorRecovery ) {
//System.err.print("[SPURIOUS] ");
return;
}
errorRecovery = true;
*/
displayRecognitionError(this.getTokenNames(), e);
}
public String getErrorMessage(RecognitionException e, String[] tokenNames) {
String msg = null;
if ( e instanceof MismatchedTokenException ) {
MismatchedTokenException mte = (MismatchedTokenException)e;
msg = "mismatched character "+getCharErrorDisplay(e.c)+" expecting "+getCharErrorDisplay(mte.expecting);
}
else if ( e instanceof NoViableAltException ) {
NoViableAltException nvae = (NoViableAltException)e;
// for development, can add "decision=<<"+nvae.grammarDecisionDescription+">>"
// and "(decision="+nvae.decisionNumber+") and
// "state "+nvae.stateNumber
msg = "no viable alternative at character "+getCharErrorDisplay(e.c);
}
else if ( e instanceof EarlyExitException ) {
EarlyExitException eee = (EarlyExitException)e;
// for development, can add "(decision="+eee.decisionNumber+")"
msg = "required (...)+ loop did not match anything at character "+getCharErrorDisplay(e.c);
}
else if ( e instanceof MismatchedNotSetException ) {
MismatchedNotSetException mse = (MismatchedNotSetException)e;
msg = "mismatched character "+getCharErrorDisplay(e.c)+" expecting set "+mse.expecting;
}
else if ( e instanceof MismatchedSetException ) {
MismatchedSetException mse = (MismatchedSetException)e;
msg = "mismatched character "+getCharErrorDisplay(e.c)+" expecting set "+mse.expecting;
}
else if ( e instanceof MismatchedRangeException ) {
MismatchedRangeException mre = (MismatchedRangeException)e;
msg = "mismatched character "+getCharErrorDisplay(e.c)+" expecting set "+
getCharErrorDisplay(mre.a)+".."+getCharErrorDisplay(mre.b);
}
else {
msg = super.getErrorMessage(e, tokenNames);
}
return msg;
}
public String getCharErrorDisplay(int c) {
String s = String.valueOf((char)c);
switch ( c ) {
case Token.EOF :
s = "";
break;
case '\n' :
s = "\\n";
break;
case '\t' :
s = "\\t";
break;
case '\r' :
s = "\\r";
break;
}
return "'"+s+"'";
}
/** Lexers can normally match any char in it's vocabulary after matching
* a token, so do the easy thing and just kill a character and hope
* it all works out. You can instead use the rule invocation stack
* to do sophisticated error recovery if you are in a fragment rule.
*/
public void recover(RecognitionException re) {
//System.out.println("consuming char "+(char)input.LA(1)+" during recovery");
//re.printStackTrace();
input.consume();
}
public void traceIn(String ruleName, int ruleIndex) {
String inputSymbol = ((char)input.LT(1))+" line="+getLine()+":"+getCharPositionInLine();
super.traceIn(ruleName, ruleIndex, inputSymbol);
}
public void traceOut(String ruleName, int ruleIndex) {
String inputSymbol = ((char)input.LT(1))+" line="+getLine()+":"+getCharPositionInLine();
super.traceOut(ruleName, ruleIndex, inputSymbol);
}
}