Re: How to remove verbosity from the data passing mechanism using alist or plist ?

[Thien-Thi Nguyen]

[cc changed to help-gnu-emacs -- this does not belong on emacs-devel]

() Fren Zeee <frenzeee@gmail.com>
() Sun, 5 Dec 2010 12:15:08 -0800

   [code]

Here is ‘find-my-marker-GOLD’, munged a bit:

(defun find-my-marker-GOLD ()
  "Starting from anywhere in the file, find my marker GOLD its value
   and location."
  (interactive)
  (save-excursion
    (save-match-data
      ;; Starting from the end of the accessible region, find GOLD.
      (goto-char (point-max))
      ;; a/ This value of this expression is discarded.
      ;;    It turns out to be the same as "location" below,
      ;;    so if you save it, you can avoid a call to ‘point’.
      ;; b/ The optional args default to ‘nil’, and can be dropped.
      (search-backward-regexp "GOLD=\\([0-9]+\\)\n" nil nil nil)

      ;; In the following, i have deleted the eol comments, which
      ;; obscure more than enlighten (on my small computer screen).

      ;; You might consider using `((k0 . ,v0)
      ;;                            (k1 . ,v1))
      ;; for succinctness (note backquote and comma placement).
      ;; An intermediate solution is to use ‘acons’.
      (list
       (list
        :GOLD-value
        ;; The ‘replace-regexp-in-string’ is not necessary.
        ;; The initial regexp match (above) already sets the match
        ;; data; you can use ‘(match-string 1)’ to retrieve it.
        (string-to-number
         (replace-regexp-in-string "GOLD=\\([0-9]+\\)\n" "\\1"  (match-string 
0))))
       (list
        :GOLD-location
        (point))))))

   [Q] Are there any defects in this method of passing struct and what
   improvements are possible ?

All defects are misalignments of intention and implementation.
If you don't know your intention clearly, it's easy for a defect
to creep in.  Improvements, likewise, depend on intention and pov.

       Specifically, are there ways to reduce verbosity without using cl
   or staying purely in elisp ?

You can use shorter variable names.  You can make your program
less piecewise-constructive and more table-oriented.

   [Q] Is there a way to avoid lengthy calling statement like
         (car (assoc-default :GOLD-value    GOLD )
       inside let,

       since the first argument of let is an alist of the form
            ((sym1 val1) (sym2 val2))

You need the ‘car’ because you do ‘(list k v)’.
If you use ‘(cons k v)’, then you do not need the ‘car’.

   [Q] Is there a way to using plists for return from find-my-marker-GOLD
       and utilize in the user function test-GOLD

Yes, but probably you will want to avoid plists.