Task

Implement the algorithm to compute the principal   nth   root   





A

n





{\displaystyle {\sqrt[{n}]{A}}}

   of a positive real number   A,   as explained at the   Wikipedia page.



 
Flush empty stack
Over 2 copy 2nd as new top (so 2nd now is 3rd)
Over 2,2 repeat Over 2 two times.
Shift 2 send top to 2nd, and 2nd to top (1st) (there is a SHFITBACK to revesre action)
Drop drop top
Number get top if is number, else raise error
Read, read a variable form top. 
Functions parameters works with a read too
     Function Root {
             Read a, n%, d as double=1.e-4
      ......
      }
because we can send any type and number if function, interpreter can make conversions if we declare that,
or if it not possible (no conversion done to a numeric variable if a string is in top of stack) we get an error.
Also if we send less values, and we didn't initialize variable before, we get error too.  
Here we need to flush stack for other parameters if from an error anyone put more arguments. 
(interpreter never count before call a user function, except for calling events by using event object,
so there there is a signature to follow)


n% is double inside.
