Here is a mickey mouse approach, I wrote some years ago..... the request was about on how to add fractional numbers i.e.
12' 5-1/2" + 6' 3-5/8" = 18' 9-1/8"
MMcal = Mickey Mouse Calculator....
(defun C:MMcal (/ key fun input inputA data r)
(initget "+ - Div")
(if (setq key (getKword "\nOperation [+/-/Div]: "))
(progn
(setq fun (eval (read key)))
(cond
((= fun +)
(while (setq input (getDist "\nInput: "))
(if input
(setq data (cons input data))))
(setq r (apply 'fun data)))
((= fun -)
(setq inputA (getDist "\nSubtract base: "))
(while (setq input (getDist "\nFollowing number: "))
(if input
(setq data (cons input data))))
(foreach i data
(setq inputA (fun inputA i)))
(setq r inputA))
((= key "Div")
(setq inputA (getDist "\nDivide base: "))
(while (setq input (getDist "\nFollowing number: "))
(if input
(setq data (cons input data))))
(foreach i data
(setq inputA (/ inputA i)))
(setq r inputA)))
(princ "\nResult: ")
(princ (rtos r (getvar "lunits") (getvar "luprec")))))
(princ))