Added the nano writer mode (prototype)

nano-writer.el

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+;; ---------------------------------------------------------------------
+;; GNU Emacs / N Λ N O - Emacs made simple
+;; Copyright (C) 2020 - N Λ N O developers 
+;;
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+;; ---------------------------------------------------------------------
+(require 'org)
+
+(defun writer-mode--num-format (numbering)
+  "Alternative numbering format for org-num.
+
+First level: 1 | xxx
+Second level: 1.1 — xxx
+Third level: 1.1.1 - xxx
+etc.
+"""
+  (if (= (length numbering) 1)
+      (propertize (concat (mapconcat
+                           #'number-to-string
+                           numbering ".") " | " )
+                  'face `(:family "Roboto Condensed"
+                          :height 250
+                          :foreground ,nano-color-faded))
+    (propertize (concat (mapconcat
+                         #'number-to-string
+                         numbering ".") " — " )
+                'face `(:family "Roboto Condensed"
+                        :foreground ,nano-color-faded))))
+
+;; Specific face for headline stars
+(font-lock-add-keywords 'writer-mode
+             '(("^*+ " 0 `(:family "Roboto Mono"
+                           :height 140
+                           :foreground ,nano-color-faded) prepend)
+               ) 'append)
+
+(defun writer-mode--compute-prefixes ()
+  "Compute prefix strings for regular text and headlines."
+
+  (setq org-indent--heading-line-prefixes
+        (make-vector org-indent--deepest-level nil))
+  (setq org-indent--inlinetask-line-prefixes
+        (make-vector org-indent--deepest-level nil))
+  (setq org-indent--text-line-prefixes
+        (make-vector org-indent--deepest-level nil))
+
+  (let* ((min-indent 5)
+         (indent (+ 1 (seq-max 
+                  (org-element-map
+                      (org-element-parse-buffer) 'headline
+                    #'(lambda (item)
+                        (org-element-property :level item))))))
+         (indent (max indent min-indent)))
+
+  (dotimes (n org-indent--deepest-level)
+    (aset org-indent--heading-line-prefixes n
+          (make-string
+           (min indent (max 0 (- indent 1 n))) ?\s))
+    (aset org-indent--inlinetask-line-prefixes n
+          (make-string indent ?\s))
+    (aset org-indent--text-line-prefixes n
+          (make-string indent ?\s)))))
+
+
+
+(define-derived-mode writer-mode org-mode "NΛNO writer"
+
+  ;; Faces
+  (face-remap-add-relative 'org-level-1
+                           :overline nano-color-subtle
+                           :family "Roboto" :height 180)
+  (face-remap-add-relative 'org-level-2
+                           :family "Roboto" :height 160)
+  (face-remap-add-relative 'org-level-3
+                           :family "Roboto" :height 150)
+
+  ;; Header line
+  (setq header-line-format nil)
+
+  ;; Layout
+  (setq fill-column 72)
+  (setq-default line-spacing 1)
+
+  ;; Indentation
+  (setq org-startup-folded nil)  
+  (org-indent-mode)
+  (setq org-level-color-stars-only nil)
+  (setq org-hide-leading-stars nil)
+  (advice-add 'org-indent--compute-prefixes :override
+              #'writer-mode--compute-prefixes)
+
+  ;; Numbering
+  (setq org-num-skip-unnumbered t)
+  (setq org-num-skip-footnotes t)
+  (setq org-num-max-level 2)
+  (setq org-num-face nil)
+  (org-num-mode)
+  (setq org-num-format-function 'writer-mode--num-format)
+
+  ;; Markup
+  (make-variable-buffer-local 'org-emphasis-alist)
+  (setq org-emphasis-alist '(("*" bold)
+                             ("/" italic)
+                             ("_" underline)
+                             ("=" org-verbatim verbatim)
+                             ("~" org-code verbatim)
+                             ("+" (:family "Roboto Slab"
+                                   :weight 'bold :height 200)))))
+
+(provide 'nano-writer)

nano-writer.org

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+
+
++NΛNO Writer Mode+
+/Nicolas P. Rougier — December 2020/
+
+*Abstract |* NΛNO writer mode is an emacs minor mode based on org-mode
+           whose goal is to offer a nice writing environment such that
+           it is not necessary to transform the document to read it,
+           GNU Emacs being the main reader.
+
+
+* Introduction   
+
+Following up my article on the design of text editors /[1]/, this is an
+experiment at designing a template for scientific article that can be
+read and interacted with directly from within GNU Emacs based on the
+all-mighty org-mode.
+
+** Alternative indentation   
+
+
+By tweaking =org-indent--compute-prefixes=, it is possible to align text
+on the left and have the leading stars in the margin.
+
+** Typography   
+
+Body font is [[https://fonts.google.com/specimen/Roboto+Mono][Roboto Mono Light]], title font is [[https://fonts.google.com/specimen/Roboto+Slab][Roboto Slab]], headers font
+is [[https://fonts.google.com/specimen/Roboto][Roboto]] and theme is [[https://github.com/rougier/nano-emacs][NΛNO light theme]] /[2]/. Line spacing is 1.
+
+** Section numbering
+
+Automatic section numbering is done using org-num-mode with a special
+format function.
+
+
+* References   
+:PROPERTIES:
+:UNNUMBERED: nil
+:END:
+
+*[1]* Rougier, N.P. 2020. *On the design of text editors*, [[https://arxiv.org/abs/2008.06030][arXiv]].
+*[2]* Rougier, N.P. 2020. *GNU Emacs / N Λ N O*, [[https://github.com/rougier/nano-emacs][GitHub]].