Removing left recursion in xtext

Question

I saw many posts on this, and also read Parsing Expressions with Xtext in https://eclipse.org/Xtext/documentation/307_special_languages.html, as well as https://typefox.io/parsing-expressions-with-xtext

However, I was not able to eliminate my LL recursion error:

My grammar is:

Was able to solve all but one issue

Trailer:
    '[' (index+=Expr)?']'|
    '(' (params+=Expr_list)? ')'|
    '.' name=id(trailer+=Trailer)* //TODO fix left recusion
;

Tried the following

Trailer:
    TerminalTrailer |
    '.' name=id (trailer+=TerminalTrailer )* //TODO fix left recusion


TerminalTrailer returns Trailer:
        '[' (index+=Expr)?']'|
        '(' (params+=Expr_list)? ')';

but this is not working , and I am a bit confused why , it is also don't account for a case that . name (Trailer) where trailer is another . name

any ideas?

Answer 1

these kind of expressions look like the following ones in Xtext

Addition returns Expression:
  Multiplication ({Addition.left=current} '+' right=Multiplication)*;

Multiplication returns Expression:
  Primary ({Multiplication.left=current} '*' right=Primary)*;

Primary returns Expression:
  NumberLiteral |
  '(' Addition ')';

NumberLiteral:
  value=INT;

see http://typefox.io/parsing-expressions-with-xtext for a detailed explanation. and https://github.com/LorenzoBettini/xsemantics/blob/master/examples/it.xsemantics.example.expressions/src/it/xsemantics/example/expressions/Expressions.xtext for a bit more complex example

Update:

your stuff could be something like (untested)

OrExpression:
    And_expr ({OrExpression.left=current} '||' right+=And_expr)*;

And_expr returns Expression:
    Subtract_expr ({And_expr.left=current} '&&' right+=Subtract_expr)*;

    Subtract_expr returns Expression:
    "!" not=Subtract_expr
    | Compare_expr;

Compare_expr returns Expression:
    Math_expr (operator+=('>=' | '<=' | '==' | '!=' | '>' | '<') comp+=Math_expr)+ |
    '(' Compare_expr ')' | // 
    Literal;

Literal returns Expression:
    {Literal}(
    value?="true" | "false");

Math_expr:
    valie=INT;

Edit 2:

Trailer:
    '[' (index+=Expr)?']'|
     '(' (params+=Expr_list)? ')'|
     '.' name=ID (=>trailer+=Trailer)*
 ;