[antlr-interest] nondeterminism in lexer rule

Abhijit Nandkumar Ghonge Abhijit_Ghonge at infosys.com
Fri Mar 2 00:59:49 PST 2007

Hi people,
I tried to create now a simple lexer file as below:


class SimpleLexer extends Lexer;
options {
  charVocabulary = '\0'..'\377';
  exportVocab = SimpleScr;   // call the vocabulary "FinScr"
  testLiterals =true;   // automatically test for literals
  k = 7;                  // eight characters of lookahead to
distinguish 'end' from 'end-->'
  caseSensitive = false;
  caseSensitiveLiterals = false;
//  filter = true;


IF	:	"if"	;

THEN	:	"then"	;

ELSE	:	"else"	;

GOTO	:	"goto"	;

DOT	:	'.'	;

	: (('a'..'z') ('a'..'z'|'0'..'9'| '_' | '@' | '$')*)

	| LITERAL {  $setType(NAME); }

But alas, I'm still getting this nondeterministic warnings:
simple.g: warning:lexical nondeterminism between rules IF and VAR_RCF
simple.g:     k==1:'i'
simple.g:     k==2:'f'
simple.g:     k==3:<end-of-token>
simple.g:     k==4:<end-of-token>
simple.g:     k==5:<end-of-token>
simple.g:     k==6:<end-of-token>
simple.g:     k==7:<end-of-token>

Basically the nextToken() method generates following code:
else if ((LA(1)=='i') && (LA(2)=='f') && (true) && (true) && (true) &&
true) && (true)) {
}else if (((LA(1) >= 'a' && LA(1) <= 'z')) && (true) && (true) && (true)
&& (true) && (true) && (true)) {

So suppose you have some statement like goto IFINIT where IFINIT is a
label. The nextToken in the above loop matches IF rather than the
complete word IFINIT and throws error [line 13:8: expecting NAME, found
'IF']. How can I develop a grammer logic wherein I will take the
complete word and then look up the literal table. Please help.

Thanks & regards,

-----Original Message-----
>If 'if' is a keyword in your language, why not using ANTLR's builtin
>support for keyword by doing "testLiterals = true"? You can use java.g
>as an example.

>  Can I put some logic wherein it will compare the whole token IFINIT
> with IF  rather character by character.
> I have declared IF as literal with following option for the grammer
> my label IFINIT/ENDSCRIPT forms part of token LITERAL which is defined

> as below:
Xue Yong Zhi
XRuby (Ruby to Java bytecode compiler):

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