Using reactors to error trap

I have used a error trap method in Autocad for a while now and it does not work in Bricscad but just not sure why not.

To explain say F12 will return a error no command but the reactor looks at the error and strips into 2 parts F & 12 so does fillet R 12 then asks for pick pts. The circle is same c23 ask for a point and draws a circle with radius 23. Please note decimal is not supported but a workaround is to do 12-5 would return 12.5