def visitConcatenation(self, ctx):
        """
        expression: expression AMPERSAND expression
        """
        arg1 = conversions.to_string(self.visit(ctx.expression(0)), self._eval_context)
        arg2 = conversions.to_string(self.visit(ctx.expression(1)), self._eval_context)
        return arg1 + arg2
expression: expression AMPERSAND expression