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Learning Emacs lisp

• Use nreverse and nconc to operate on lists in-place.
• Set buffer local variables:

(setq-local my-clever-var)

• Execute before saving buffer:

(add-hook 'write-file-hooks
          (lambda ()
            (message "about to save!")))

• Possibly use to start processes and send file content:

(make-comint NAME PROGRAM &optional STARTFILE &rest SWITCHES)

• Creating markers:

(setq my-marker (copy-marker (point)))
  #<marker at 10251 in *ielm*>

(marker-buffer my-marker)
  #<buffer *ielm*>

(marker-position my-marker)
  10251 (#o24013, #x280b, ?⠋)

• Get org heading at point:

(org-get-heading 'no-tags 'no-todo)

• Remove string text properties. From manual:

(substring-no-properties STRING &optional FROM TO)

Return a substring of STRING, without text properties. It starts at index FROM and ends before TO. TO may be nil or omitted; then the substring runs to the end of STRING. If FROM is nil or omitted, the substring starts at the beginning of STRING. If FROM or TO is negative, it counts from the end.

• Skip org entry metadata/drawers:

(org-end-of-meta-data-and-drawers)

• Random access to org entry using id (or CUSTOM_ID):

(org-open-link-from-string "[[#%exciting-custom-id]]")

• From Debugging Elisp Part 1: Earn your independence:

• Go to where the function is defined.
• Press C-u C-M-x. Edebug breakpoint for function.
• Invoke function in question.
• n/c will get you around.
• q when done.

• Pretty printing objects:

(let ((my-var (list "val1"
                    "val2"
                    "val3")))
  (pp-to-string my-var))

• Search and/or replace in curent buffer:

(re-search-forward "needle"
                   nil t)
(match-beginning 0) ;; Start location of match from last search.
(match-end 0) ;; End location of match from last search.
(replace-match "love")

;; needle-in-haystack

• Restrict buffer editing to a region:

(narrow-to-region (point)
                  (point-max))

• Restore restriction:

(save-restriction (narrow-to-region (point)
                                    (point-max))

• Restore point, mark, and current buffer:

(save-excursion (goto-char (point-max))
                (insert "Hello elisp."))

• Concatenating strings:

(concat "Hello " "elisp " "world.")

• Grabbing thing at point:

(thing-at-point 'word)
(thing-at-point 'symbol)
(thing-at-point 'line)

• Unit test with ert.
• Basic iteration with dolist:

(dolist (v '("a" "b" "c"))
  (print v))

• Output to other buffer:

(with-current-buffer (get-buffer-create "*some buffer*")
  (princ '(some list to print)
         (current-buffer)))

• For a temporary buffer, use with-temp-buffer:

(with-temp-buffer
  (insert "abc")
  (point))

• Cons cells bookmark.
• Check for substring:

(string-match-p REGEXP STRING &optional START)

• Matching substrings and accessing groups:

(setq haystack "Always click [[http://reddit.com/r/emacs][here]].")
(setq needle-re "\\[\\[\\(.*\\)]\\[\\(.*\\)]]")
  "\\[\\[\\(.*\\)]\\[\\(.*\\)]]"

(string-match needle-re haystack)
  13 (#o15, #xd, ?\C-m)

(match-string 0 haystack)
  "[[http://reddit.com/r/emacs][here]]"

(match-string 1 haystack)
  "http://reddit.com/r/emacs"

(match-string 2 haystack)
  "here"

• Return argument unchanged (noop):

(identity ARG)

• Org insert today's timestamp

(org-insert-time-stamp (current-time))

• OS version in .emacs: Determine OS in emacs lisp.
• First element

(car LIST)

• All but first element

(cdr LIST)

• Add NEWELT to front of PLACE

(push NEWELT PLACE)

• Invoke 'FUNCTION for each in SEQUENCE

(mapcar FUNCTION SEQUENCE)

• Search/replace

(while (search-forward "Hello")
  (replace-match "Bonjour"))

• Save to kill ring = copy.
• Point = cursor position.
• Mark = a buffer position.
• Kill = cut text.
• Yank = paste.
• Buffer:File = 1:1.
• Window:Buffer = 1:1.
• Frame:Window = 1:many.
• Font lock = syntax highlighting.