How to avoid the spaces between two texts while parsing using antlr

Question

Please help me with the following case. I have a line with multiple texts in it. Based on some rule I need to parse each words in the line. Below is my example input line

@@ KEYWORD = MyName MyAliasName

Below is my parsing rule sets.

rule1:
Keyword name = identifier{ $name.str;} (' '* diffName = identifierTest { $diffName.str; })?
;

identifier:
returns [string str]
@init{$str="";}: 
i=Word{$str+=$i.text;} (i=(Number | Word ) {$str+=$i.text;})*
;

Keyword: SPACE* START SPACE* 'KEYWORD' SPACE* EQUAL SPACE*;
Number:DIGIT+;
Word:LETTER+;

fragment LETTER: 'A'..'Z' | 'a'..'z' | '_';
fragment DIGIT: [0-9];
fragment SPACE: ' ' | '\t';
fragment START: '@@';
fragment EQUAL: '=';

The "rule1" rule defines that, the MyName text is mandatory and MyAliasName is an optional one. The "identifier" rule defined that, the name can start with only by a letter or underscores.

The Problem If I give exactly one space between MyName and MyAliasName then the above rules works fine. Whereas if there are more than one spaces between MyName and MyAliasName, then the first identifier rule reads both the texts together as MyNameMyAliasName(it removes the spaces automatically). Why ? I don't know what I'm doing wrong!

Whenever the optional texts is available then i will have to overwrite the name with AliasName. Please help and thanks in advance

Answer 1

This grammar should solve your problem

grammar TestGrammar;

rule1:
keyword name=IDENT{ System.out.println($name.text);} ( diffName = IDENT { System.out.println($diffName.text); })?
;

keyword:  START KEYWORD EQUAL;

KEYWORD : 'KEYWORD' ;

fragment LETTER: 'A'..'Z' | 'a'..'z' | '_';
fragment DIGIT: '0'..'9';
IDENT   : LETTER (LETTER|DIGIT)*;

START   : '@@';
EQUAL   : '=';
SPACE   : [ \t]+ -> skip;