现有一段select statement的代码，想用macro和循环写得更简洁些：
select;
    when (price > midpoint0) sign=1;
    when (price < midpoint0) sign=-1;
    when (symbol ne lagsymbol1) sign=1;
    when (price > lagprice1) sign=1;
    when (price < lagprice1) sign=-1;
    when (symbol ne lagsymbol2) sign=1;
    when (price > lagprice2) sign=1;
    when (price < lagprice2) sign=-1;
    when (symbol ne lagsymbol3) sign=1;
    when (price > lagprice3) sign=1;
    when (price < lagprice3) sign=-1;
    when (symbol ne lagsymbol4) sign=1;
    when (price > lagprice4) sign=1;
    when (price < lagprice4) sign=-1;

（略）
    when (symbol ne lagsymbol50) sign=1;
    when (price > lagprice50) sign=1;
    when (price < lagprice50) sign=-1;
    otherwise sign=0;
  end;


我初步试过这样写：
%macro lr(counter);
    %do d=1 %to &counter;
    when (symbol ne lagsymbol&d ) sign=1;
    when (price > lagprice&d ) sign=1;
    when (price < lagprice&d ) sign=-1;
    %end;
%mend;

select;
    when (price > midpoint0) sign=1;
    when (price < midpoint0) sign=-1;
    %lr(50);
    otherwise sign=0;
  end;
但是总是报错，说%lr(50)那里expecting WHEN, OTHERWISE or END。也就是说在select statement内部无法激活这个macro。那请问各位大大，有没有别的办法来优化我原本的代码呢？