.emacs.d/doc/emacs-notes.org

#+title: Notes on Emacs
#+author: Daniel

* Introduction to Babel

Tutorial from http://orgmode.org/worg/org-contrib/babel/intro.html

** Source Code Execution

#+begin_src hy
  (print "Hello, There!")
#+end_src

#+RESULTS:
: Hello, There!

#+begin_src sh
  echo "This file takes up `du -h emacs-org-babel-tutorial.org | sed 's/\([0-9k]*\)[ ]*emacs-org-babel-tutorial.org/\1/'`"
#+end_src

#+RESULTS:
: This file takes up 4.0K

#+begin_src R :colnames yes
  words <- tolower(scan("emacs-org-babel-tutorial.org", what="", na.strings=c("|",":")))
  t(sort(table(words[nchar(words) > 3]), decreasing=TRUE)[1:10])
#+end_src

#+RESULTS:
| #+begin_src | #+end_src | #+results: | date | plus | today's | :results | hello, | import | is") |
|-------------+-----------+------------+------+------+---------+----------+--------+--------+------|
|           5 |         5 |          4 |    3 |    3 |       3 |        2 |      2 |      2 |    2 |

*** Capturing the Results of Code Evaluation

#+begin_src python :results value
  import time
  print("Hello, today's date is %s" % time.ctime())
  print("Two plus two is")
  return 2 + 2
#+end_src

#+RESULTS:
: 4

#+begin_src python :results output
  import time
  print("Hello, today's date is %s" % time.ctime())
  print("Two plus two is")
  2 + 2
#+end_src

#+RESULTS:
: Hello, today's date is Sun Jun 26 16:04:36 2016
: Two plus two is

*** Session-based Evaluation

Have a look into /Emacs Speaks Statistics/

*** Arguments to Code Blocks

#+name: square
#+header: :var x = 0
#+begin_src python
  return x*x
#+end_src

#+call: square(x=6)

#+RESULTS:
: 36

#+tblname: fibonacci-inputs
| 1 | 2 | 3 | 4 |  5 |  6 |  7 |  8 |  9 | 10 |
| 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 |

#+name: fibonacci-seq
#+begin_src emacs-lisp :var fib-inputs=fibonacci-inputs
  (defun fibonacci (n)
    (if (or (= n 0) (= n 1))
        n
      (+ (fibonacci (- n 1))
         (fibonacci (- n 2)))))

  (mapcar (lambda (row)
            (mapcar #'fibonacci row))
          fib-inputs)
#+end_src

#+RESULTS: fibonacci-seq
| 1 | 1 | 2 |  3 |  5 |   8 |  13 |  21 |   34 |   55 |
| 1 | 3 | 8 | 21 | 55 | 144 | 377 | 987 | 2584 | 6765 |

*** In-line Code Blocks

In-line code can be call without header arguments (like so: src_sh{date}) or
with header arguments (like so: src_python[:results value]{return 10 + 10}).

*** Code Block Body Expansion

Preview: =C-c C-v v=, bound to =org-babel-expand-src-block=

#+tblname: data
| username | john-doe |
| password | abc123   |

#+begin_src emacs-lisp :var data=data
(setq my-special-username (first (first data)))
(setq my-special-password (first (second data)))
#+end_src

*** A Meta-programming Language for Org-mode

#+name: directories
#+begin_src sh :results replace
  cd ~ && du -sc * | grep -v total
#+end_src

#+RESULTS: directories
|   538604 | Desktop   |
| 77332656 | Documents |
|  1206668 | Mail      |
|        8 | News      |

#+name: directory-pie-chart
#+begin_src R :session R-pie-example :var dirs=directories
  pie(dirs[,1], labels = dirs[,2])
#+end_src

#+RESULTS: directory-pie-chart

Note: the syntax =#+name: directory-pie-chart(dirs=directories)= did not work.

*** Using Code Blocks in Org Tables

**** Example 1: Data Summaries Using R

#+name: tbl-example-data
#+begin_src R
  runif(n=5, min=0, max=1)
#+end_src

#+name: R-mean
#+begin_src R :var x=""
  colMeans(x)
#+end_src

#+tblname: summaries
|              mean |
|-------------------|
| 0.574235895462334 |
#+TBLFM: @2$1='(org-sbe "R-mean" (x "tbl-example-data()"))

**** Example 2: Babel Test Suite

/No notes/

** The Library of Babel

#+lob: square(x=6)

Does not do what I expected …

** Literate Programming

#+name: hello-world-prefix
#+begin_src sh :exports none
  echo "/-----------------------------------------------------------\\"
#+end_src

#+name: hello-world-postfix
#+begin_src sh :exports none
  echo "\-----------------------------------------------------------/"
#+end_src

#+name: hello-world
#+begin_src sh :tangle hello.sh :exports none :noweb yes
  <<hello-world-prefix>>
  echo "|                       hello world                         |"
  <<hello-world-postfix>>
#+end_src

Tangling with =C-c C-v t=.

** Reproducible Research

* Random Notes
** How to paste then copy                                              :NOTE:
:PROPERTIES:
:CREATED: [2018-08-11 Sat 21:47]
:END:
:LOGBOOK:
CLOCK: [2018-08-11 Sat 21:47]--[2018-08-11 Sat 21:48] =>  0:01
:END:

Question: how to set a mark such that all subsequent copy operations move their
text to that exact mark.

Answer: use ~cua-selection-mode~!  See
https://www.reddit.com/r/emacs/comments/8ekz0u/how_to_pastethencopy/.

/Update/: turns out it doesn’t work so well, disabled it again.
** Tramp and Telnet over non-standard ports                            :NOTE:
:PROPERTIES:
:CREATED: [2018-12-29 Sat 15:58]
:END:

Syntax: ~/telnet:HOST#PORT:~, works also with other protocols.

** Magit Walkthrough                                                   :NOTE:
:PROPERTIES:
:CREATED: [2018-08-11 Sat 21:05]
:END:

https://emacsair.me/2017/09/01/magit-walk-through/
** Fractals in Emacs                                                   :NOTE:
:PROPERTIES:
:CREATED: [2018-08-04 Sat 13:01]
:END:
:LOGBOOK:
CLOCK: [2018-08-04 Sat 13:01]--[2018-08-04 Sat 13:03] =>  0:02
:END:

From https://nullprogram.com/blog/2012/09/14/

#+begin_src emacs-lisp
(defun sierpinski (s)
  (pop-to-buffer (get-buffer-create "*sierpinski*"))
  (fundamental-mode) (erase-buffer)
  (labels ((fill-p (x y)
                   (cond ((or (zerop x) (zerop y)) "0")
                         ((and (= 1 (mod x 3)) (= 1 (mod y 3))) "1")
                         (t (fill-p (/ x 3) (/ y 3))))))
    (insert (format "P1\n%d %d\n" s s))
    (dotimes (y s) (dotimes (x s) (insert (fill-p x y) " "))))
  (image-mode))

(defun mandelbrot ()
  (pop-to-buffer (get-buffer-create "*mandelbrot*"))
  (let ((w 400) (h 300) (d 32))
    (fundamental-mode) (erase-buffer)
    (set-buffer-multibyte nil)
    (insert (format "P6\n%d %d\n255\n" w h))
    (dotimes (y h)
      (dotimes (x w)
        (let* ((cx (* 1.5 (/ (- x (/ w 1.45)) w 0.45)))
               (cy (* 1.5 (/ (- y (/ h 2.0)) h 0.5)))
               (zr 0) (zi 0)
               (v (dotimes (i d d)
                    (if (> (+ (* zr zr) (* zi zi)) 4) (return i)
                      (psetq zr (+ (* zr zr) (- (* zi zi)) cx)
                             zi (+ (* (* zr zi) 2) cy))))))
          (insert-char (floor (* 256 (/ v 1.0 d))) 3))))
    (image-mode)))
#+end_src