[antlr-interest] Confused about backtracking

[franck102]

I could really use any ideas on this, what I am beginning to understand is
that backtracking can give up on an alternative to try the next alternative
in the same rule, but if a rule at the bottom of the call chain picks an
alternative, and the invoking rule at the top subsequently can't find a
continuation, backtracking won't be able to question the earlier choice of
the bottom-most rule.

Refactoring would basically imply rewriting the entire grammar and doing two
complete passes to end up with a meaningful AST, I am hoping this is a
common problem and maybe there are patterns that can help (e.g. using
context, scopes, ...)?

Here is a toy grammar that exhibits the problem, it is unable to parse input
such as a=b. c=d;

I would like the parser, after matching a=b.c as an expr, to realize that
"=d;" can't be matched and to go back to match a=b instead...

Any suggestion greatly appreciated!
================================
grammar Test;

options {
        output=AST;
        backtrack=true;
}

program
        : statement* EOF
        ;
       
statement
        : objectExpr '=' objectExpr
        | sep
        ;
        
varDeclaration
	:	ident 'is' 'a' ident;
	
objectExpr
	:	indexExpr
	|	objectExpr DOT indexExpr
	;
	
indexExpr
	:	ident ( '[' objectExpr ']' | '(' objectExpr ')' )*
	;
	
sep : ';' | DOT;

ident	:	ID | UNIT;

// LEXER
// ==========================================

UNIT	:	'second' 's'?
	|	'minute' 's'?
	;
	
DOT	:	'.';

ID
        : ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_')*
        ;

       
WS  :   ( ' '
        | '\t'
        | '\r'
        | '\n'
        ) {$channel=HIDDEN;}
    ; 

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