t=table(1 1.1 1.3 1.4 1.5 1.7 as a,0.2 0.2 0.2 0.2 0.2 0.2 as b,["iif(a>1,min(a-1,b),0)","iif(a>1,min(a-2,b),0)","iif(a>1,min(a-3,b),0)","iif(a>1,min(a-4,b),0)","iif(a>1,min(a-5,b),0)","iif(a>1,min(a-6,b),0)"] as v)
例如，我定义了一个表如上，v 字段存储了每行的计算公式，如何通过元编程实现每行按不同的计算公式计算？
利用 parseExpr 可以传入字典赋值的特性:
each(def(mutable d)->parseExpr(d.v, d.erase!(`v)).eval(), t)
