;; Licensed under a Creative Commons Attribution 4.0 International License.
;; See http://creativecommons.org/licenses/by/4.0/
;;
;; Author: Howard X. Abrams <http://gitlab.com/howardabrams>
;; Maintainer: Howard X. Abrams
;; Created: October 18, 2024
;;
;; While obvious, GNU Emacs does not include this file or project.
;;
;; *NB:* Do not edit this file. Instead, edit the original literate file at:
;; /Users/howard.abrams/src/hamacs/ha-demos.org
;; And tangle the file to recreate this one.
;;
;;; Code:
#+end_src
* Introduction
Once made demonstrations /within/ Emacs with my [[https://github.com/howardabrams/demo-it][demo-it]] project. While on MELPA, I wanted to use my own cloned version to make sure I can keep debugging it.
Used to use [[https://github.com/takaxp/org-tree-slide][org-tree-slide]] for showing org files as presentations. Converted to use [[https://github.com/rlister/org-present][org-present]]. I love the /hooks/ as that makes it easier to handle. My concern with =org-present= is how it solely displays top-level headers.
#+begin_src emacs-lisp
(use-package org-present
:config
(defvar ha-org-present-mode-line mode-line-format "Cache previous mode-line format state")
(defun ha-org-blocks-hide-headers ()
"Make the headers and other block metadata invisible.
Instead of executing a sequence of demonstration steps, demonstrations key on “state”, that is, the active buffer or major-mode, or the heading of an Org file, etc. I described the [[https://howardism.org/Technical/Emacs/demonstrations-part-two.html][guts of writing this code]], but we bind a key to calling =ha-demo-step= with a list of /state matchers/ to functions to call when matched. For instance:
To make the contents of the expression easier to write, the =define-ha-demo= as a macro. Otherwise we write a complicated =cond= with lots of duplicated calls to =ha-demo-state-match= (defined later). This macro creates a function, so the first parameter is the name of the function:
#+BEGIN_SRC emacs-lisp
(defmacro define-ha-demo (demo-name &rest forms)
"Create a demonstration sequence as DEMO-NAME function.
Call DEMO-NAME (as an interactive function), executes a function based matching list of states at point.
Where FORMS is an even number of _matcher_ and _function_ to call.
Probably best to explain this in an example:
(define-demo demo1
(:buffer \"demonstrations.py\") (message \"In a buffer\")
The matching function, =ha-demo-state-match= looks in a cache, the =demo-prev-state= hash table, for the number of times we have triggered that state, and /add/ that value into a new state variable we use to match, =:itful-state= (yeah, naming is hard).
*Note:* If we match, we want to return non-nil, and update this new incremented value back in our cache:
#+BEGIN_SRC emacs-lisp
(defun ha-demo-state-match (triggers state)
"Return non-nil if STATE contains all TRIGGERS.
The state also includes the number of times the triggers
matched during previous calls. We do this by keeping track
of the number of successful calls, and incrementing
the iteration... if this function returns non-nil."
;; If the first element is either parameter is NOT a list,
;; we group it into a list of tuples:
(when (not (listp (car triggers)))
(setq triggers (seq-partition triggers 2)))
(when (not (listp (car state)))
(setq state (seq-partition state 2)))
(let* ((iteration (gethash state ha-demo-prev-state 0))
(itful-state (cons `(:i ,iteration) state)))
(when (ha-demo-match triggers itful-state)
(puthash state (1+ iteration) ha-demo-prev-state))))
#+END_SRC
Notice the two =when= expressions for using =seq-partition= for converting a /property-style/ list like =(:a 1 :b 2 :c 3)= into an more standard /associative/ list, like =((:a 1) (:b 2) (:c 3))=.
But can I check if I have triggered a state once before? Let’s keep track of the /states/ that have returned true before, in a hash table where the key is the /state/ (a list of =:buffer=, =:mode=, =:heading=, etc.) and the /value/ is the number of times triggered at that state:
"Matched states in keys, and store number of matches as values.")
#+END_SRC
Now, we have a new match function takes the /state/ and /triggers/, where the trigger could include an /iteration/, =:i= that limits a match. For instance:
- =(:buffer "foobar.txt" :i 0)= :: triggers the first time we call this function in this buffer.
- =(:buffer "foobar.txt" :i 1)= :: triggers the second time we call this function in this buffer.
If the =triggers= doesn’t contain an =:i=, it matches every time when meeting the other conditions.
Let’s create a function that could accept a list of /triggering keys/, and then compare that with another list representing the “current state” of the point, including the buffer, the mode, or the heading in an Org file. In this case, the magic happens by calling =seq-difference=:
#+BEGIN_SRC emacs-lisp
(defun ha-demo-match (triggers state)
"Return t if all elements of TRIGGERS are in STATE.
Where TRIGGERS and STATE are lists of key/value tuple
