How can I make a function that interactively passes a time to run-at-time?

Question

I want to make a function that calls run-at-time while setting its repeat to nil. The only thing I want to be asked to supply is the duration after which run-at-time should call a function.

Evaluating the following does what I want except for interactively asking me to input the duration: (run-at-time "120 min" nil 'my-custom-command)

None of my attempts to turn this into an interactive function have succeeded.

I have tried the following:

(defun foo ()
  (interactive)
  (call-interactively 'run-at-time 'my-custom-command))

However, evaluating this causes me to be asked to input run-at-time's repeat variable and the function to be called, neither of which I wish to supply. Putting 'nil' after 'run-at-time' to bypass the request for the repeat interval returns a "too many arguments" error message.

I have experimented within the forms of run-at-time (run-at-time TIME REPEAT FUNCTION &rest ARGS) and call-interactively (call-interactively FUNCTION &optional RECORD-FLAG KEYS), but to no avail.

I have also tried using the "s" and "n" flags (perhaps incorrectly) in case they might allow a string or a number to supply run-at-time's duration, but though this results in a string or a number being asked for, supplying either returns an error message.

What would make this function work?

Answer 1

You don’t need or want call-interactively. You just want to supply enough information to interactive to prompt for a single value, and then call run-at-time with that value:

(defun foo (time)
  (interactive "sRun at time: ")
  (run-at-time time nil 'my-custom-command))