Looks like I'm in half sleep today :-) Previous explanation (that the problem
is in the lexer) is infact correct.
Try running a test program which just gets all tokens from the lexer and does
no parsing as shown below:
public class __Test__ {
public static void main(String args[]) throws Exception {
TestLexer lex = new TestLexer(new
ANTLRFileStream("/root/workspace/Test/output/__Test___input.txt"));
CommonTokenStream tokens = new CommonTokenStream(lex);
tokens.getTokens();
}
}
With the input "1.", I get the error
line 1:2 required (...)+ loop did not match anything at character '<EOF>'
- Indhu
----- Original Message -----
From: Indhu Bharathi <[email protected]>
To: Thomas Woelfle <[email protected]>
Cc: [email protected]
Sent: Wednesday, February 18, 2009 2:32:49 PM GMT+0530 Asia/Calcutta
Subject: Re: [antlr-interest] Problem when parsing numerics
Well.. There is a bug in my explanation. I got confused with a problem I was
facing. Your problem is actually simpler. Here goes the explanation.
Lexer sees "1." and since lexer always forms tokens with max string length
possible it forms a token NUMERIC with the string "1." and this comes to your
parser. But what your parser is expacting is NUMERIC followed by a '.'. So
parsing fails. Simple.
- Indhu
----- Original Message -----
From: Indhu Bharathi <[email protected]>
To: Thomas Woelfle <[email protected]>
Cc: [email protected], [email protected]
Sent: Wednesday, February 18, 2009 2:27:19 PM GMT+0530 Asia/Calcutta
Subject: Re: [antlr-interest] Problem when parsing numerics
The following grammar will fix your problem.
-------------------------------------------
grammar Test;
options {language=Java;}
foo : numeric DOT;
numeric : NUMBER (DOT NUMBER)?;
NUMBER : '0'..'9'+
;
DOT : '.'
;
--------------------------------------------
I dont know the exact reason why this occours. Will try my best to explain.
The lexer will always try to form a token with maximum string length possible.
In this case (1.) , on seeing a '.' the lexer 'predicts' it to be '0'..'9'+
('.' '0'..'9'+) assuming the second part (under ?) is present and runs the DFA
and the DFA crashes. I guess it is generally not a good idea to have two rules
R1 and R2 in lexer where R1 starts with R2.
Will be good if someone can add more clarity to the explanation.
- Indhu
----- Original Message -----
From: Thomas Woelfle <[email protected]>
To: [email protected]
Cc: [email protected]
Sent: Wednesday, February 18, 2009 1:21:02 PM GMT+0530 Asia/Calcutta
Subject: Re: [antlr-interest] Problem when parsing numerics
Hi Jim,
thanks for the tip. This lexer grammar for floating points is quite
impressive and answers some interesting questions to me. But it did not
solve my problem. Using the toekn rule 'FLOATING_POINT_LITERAL' in my
grammar results in the same MismatchedTokenException. My adjusted
grammar is:
foo : FLOATING_POINT_LITERAL '.';
where "FLOATING_POINT_LITERAL" is the rule from your example.
Parsing the input string "1.5." results in a MismatchedTokenException.
Any idea what is going wrong?
Regards,
Thomas
> Thomas Woelfle wrote:
>
>> Hi,
>>
>> I've been running into a strange problem using ANTLR 3.1.1. I don't know
>> wether it is a bug in my grammar or a bug in ANTLR.
>> In the language that has to be parsed following lines are legal strings:
>>
>> 1.
>> 1.5.
>>
>> There is a rule where a numeric is followed by a dot.
>>
>>
> Please look in the FAQ/examples:
>
> http://www.antlr.org/wiki/display/ANTLR3/Lexer+grammar+for+floating+point%2C+dot%2C+range%2C+time+specs
>
>
> You should be able to simplify the grammar here to just what you need.
>
> Jim
>
> List: http://www.antlr.org/mailman/listinfo/antlr-interest
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