Antlr4.Analysis.LeftRecursiveRuleAnalyzer.StripLeftRecursion C# (CSharp) Method

        public virtual GrammarAST StripLeftRecursion(GrammarAST altAST)
        {
            GrammarAST lrlabel = null;
            GrammarAST first = (GrammarAST)altAST.GetChild(0);
            int leftRecurRuleIndex = 0;
            if (first.Type == ELEMENT_OPTIONS)
            {
                first = (GrammarAST)altAST.GetChild(1);
                leftRecurRuleIndex = 1;
            }

            ITree rref = first.GetChild(1); // if label=rule
            if ((first.Type == RULE_REF && first.Text.Equals(ruleName)) ||
                 (rref != null && rref.Type == RULE_REF && rref.Text.Equals(ruleName)))
            {
                if (first.Type == ASSIGN || first.Type == PLUS_ASSIGN)
                    lrlabel = (GrammarAST)first.GetChild(0);
                // remove rule ref (first child unless options present)
                altAST.DeleteChild(leftRecurRuleIndex);
                // reset index so it prints properly (sets token range of
                // ALT to start to right of left recur rule we deleted)
                GrammarAST newFirstChild = (GrammarAST)altAST.GetChild(leftRecurRuleIndex);
                altAST.TokenStartIndex = newFirstChild.TokenStartIndex;
            }

            return lrlabel;
        }