private static TransitionConditionExpr Translate(this exprItem item, AutomatonParsingContext ctx)
        {
            TransitionConditionExpr expr;

            if (item.identifier != null)
            {
                expr = new TransitionConditionExpr.VarExpr(ctx.Unescape(item.identifier.@string));
            }
            else if (item.exprGroup != null)
            {
                expr = item.exprGroup.exprSeq.TranslateToConditionExpr(ctx);
            }
            else if (item.literal != null)
            {
                expr = new TransitionConditionExpr.ConstExpr(true);
            }
            else
            {
                throw new NotImplementedException();
            }

            if (item.not != null)
            {
                expr = new TransitionConditionExpr.NotExpr(expr);
            }

            return(expr);
        }
 bool ITransitionConditionExprVisitor <bool> .VisitNot(TransitionConditionExpr.NotExpr not)
 {
     return(false);
 }
 VarsCollector ITransitionConditionExprVisitor <VarsCollector> .VisitNot(TransitionConditionExpr.NotExpr not)
 {
     throw new InvalidOperationException();
 }
 bool ITransitionConditionExprVisitor <bool> .VisitNot(TransitionConditionExpr.NotExpr not)
 {
     return(!not.Child.Apply(this));
 }