🚀 go-pugleaf

Here's the way I've written the general form.  Now that I've got it, I
can't figure out how I managed without it!

(defun read-object (prompt acceptable &optional initial-contents)
  "Return an object read from the minibuffer.
Prompt with the string PROMPT and use the function ACCEPTABLE to decide if
entered item is acceptable.  If non-nil, optional third arg INITIAL-CONTENTS
is a string to insert in the minibuffer before reading."
  (let ((value (read-minibuffer prompt initial-contents)))
    (while (not (funcall acceptable value))
      (setq value (read-minibuffer prompt initial-contents)))
    value))


For example, to read a month, defaulting to current-month, use

    (read-object
      "Enter month (1-12): "
      '(lambda (x) (and (integerp x) (<= 1 x) (<= x 12)))
      (int-to-string current-month))