[antlr-interest] lexer problem...

[Jim Idle]

I think that this question points out that many of us expect ATNLR to
"just work it out" for us. All these problems are best solved with a
mind experiment first "How would you scan it with the eye?", then break
the rule at the different alternatives yourself and stick in the
lookahead you perform with your mind. It will result in better generated
code anyway:

 

grammar fred;

 

stat 

            : test+

            ;

test

            :           (INT DOT ID)

            |           FLOAT

            ;

            

fragment

DIGIT    : '0'..'9'

            ;

 

FLOAT : INT

                                    (

                                                  ('.' INT)=> '.' INT

                                                | {$type = INT; }

                                    )

                        ;

 

DOT     : '.' ;

                        

Fragment                                  // Also ensures a token type
INT is present

INT       : DIGIT+;

 

ID         :           ('A'..'Z' | 'a'..'z')+

            ;

 

Jim

 

From: antlr-interest-bounces at antlr.org
[mailto:antlr-interest-bounces at antlr.org] On Behalf Of Lloyd Dupont
Sent: Thursday, July 19, 2007 6:13 AM
To: antlr-interest at antlr.org
Subject: [antlr-interest] lexer problem...

 

I have the following lexer rule:

==============

FLOAT : ('0'..'9')+ '.' ('0'..'9')+ (EXPONENT_PART)?
(FLOAT_TYPE_SUFFIX)?
 ;
==============

as you can see: it require 1 or more number on both side of the DOT

 

my problem is that with the follwoing input:

 

 

====

1.ToString()

====

 

instead of returning INT DOT ID

it apparently try to return a FLOAT and I have the following error
message when trying on the command line:

====

line 1:2 required (...)+ loop did not match anything at character 'T'

====

 

Any idea how to solve this lexer problem??

 

Thanks! :D

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