accept a single character with a default value? read-char with default value?

Question

How can I read a single input from minibuffer ,
and provide a default value at the same time so he can just enter to accept?

Answer 1

(string-to-char
  (read-string "Char (or the first char of your input string): "
               nil nil
               ;; Default:
               "👀"))

If you use functions like read-char, it will be difficult to distinguish between the default value and the keystroke of <return>. (You cannot use C-q, because it just issues the char ?\C-q.