Re: Operating the HIST feature of completing-read

[Jean Louis]

* carlmarcos--- via Users list for the GNU Emacs text editor 
<help-gnu-emacs@gnu.org> [2022-07-11 03:23]:
> How does HIST work when using completing-read?  Any examples that
> would help me with this?

I find HIST variables a waste in coding, so I am automating it by
automatically assigning HIST variable to every call to the function.

(defun rcd-symbol-if-not-exist (variable &optional value description)
  "Return symbol for VARIABLE. 

It will generate new VARIABLE if it does not exist."
  (let* ((variable (replace-regexp-in-string "[^[:alnum:]]" "-" (downcase 
variable)))
         (rcd-symbol (intern variable))
         (description (or description (format "Generated variable `%s'" 
variable))))
    (if (boundp rcd-symbol)
        rcd-symbol
      (eval (list 'defvar rcd-symbol value description)))))

(defun rcd-ask-history-variable (prompt)
  "Generate history variable for PROMPT."
  (let* ((description (format "History for `%s' prompt." prompt)))
    (rcd-symbol-if-not-exist (concat "rcd-" prompt "-history") nil 
description)))

Then there is my wrapper function for `completing-read`:

(defun rcd-choose (list &optional prompt predicate initial-input def)
  "Ask user for LIST of choices.
If only one element, function `y-or-n-p' will be used.
For multiple elements `completing-read' is used.

If nothing chosen it will return empty string."
  (let* ((completion-ignore-case t)
         (prompt (or prompt "Choose: "))
         (description (format "History for `%s' completion prompt." prompt))
         (history (rcd-symbol-if-not-exist (concat "rcd-" prompt "-history") 
nil description))
         (input (cond ((length= list 1) (if (y-or-n-p (nth 0 list)) (nth 0 
list) ""))
                      (t (rcd-repeat-until-not-empty-string 'completing-read 
prompt list predicate t initial-input history def t)))))
    input))

That generates history variables automatically in the line, based on
the prompt:

(history (rcd-symbol-if-not-exist (concat "rcd-" prompt "-history") nil 
description))

Then this below would use history variable: rcd-choose---history

(rcd-choose '("One" "Two" "Three"))

because following evaluates to that symbol:

(rcd-symbol-if-not-exist (concat "rcd-" "Choose: " "-history") nil "History for 
`Choose: ' completion prompt.") ⇒ rcd-choose---history

However, any other prompt would yield automatically with a different
history variable based on its prompt like "Choose a number: "

(rcd-choose '("One" "Two" "Three") "Choose a number: ") ⇒ "One"


-- 
Jean

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