Re: Checking parameters

[Lennart Borgman (gmail)]

Cecil Westerhof wrote:
> I am new to Emacs and lisp.
> What is the best way to check parameters and do error handling when they are
> not correct?
>
> I have the following function:
> (defun getHours(time)
>   (interactive "sHH:MM: ")
>   (let ((timelist (split-string time ":")))
>     (+
>       (string-to-number (car timelist))
>       (/
>         (string-to-number (cadr timelist))
>         60.0
>       )
>     )
>   )
> )
>
> How do I check that there is exactly one parameter? And how do I check the
> format and give an error that works in interactive and normal mode?
> For example when I give
>     (getHours "0:120")
> I get
>     2.0
> How should I generate an error/exception?


You probably want to use the most simple way, something like

(defun get-hours(time)
  (interactive "sHH:MM: ")
  (let ((timelist (split-string time ":"))
        (errmsg "Time format error"))
    (unless (= (length (nth 1 timelist)) 2)
      (error errmsg))
    (+
      (string-to-number (nth 0 timelist))
      (/
        (string-to-number (nth 1 timelist))
        60.0))))