I'm not sure if you misunderstood them or I misunderstood you, but there's no legitimate reason you can't filter on computed columns as is: w = employee(name

I'm not sure if you misunderstood them or I misunderstood you, but there's no legitimate reason you can't filter on computed columns as is: w = employee(name == "Jones")[comp = salary / (age - 18)](comp > 2000)