Emacs Lisp

https://www.gnu.org/software/emacs/manual/html_node/eintr/
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Emacs Lisp is a dialect of the Lisp programming language designed for extending, configuring, and...
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### Start Emacs with -Q -D options

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Simple-Extension.html

Command line options to start Emacs with a clean configuration.

```bash
emacs -Q -D
```

--------------------------------

### Installation list for print-Y-axis test

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/print_002dY_002daxis-Penultimate.html

Lists the functions to install before testing print-Y-axis.

```emacs-lisp
Y-axis-label-spacing
Y-axis-tic
Y-axis-element
Y-axis-column
print-Y-axis

```

--------------------------------

### Usage examples of nth

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/nth.html

Examples demonstrating how to retrieve elements from a list using zero-based indexing with nth.

```emacs-lisp
(nth 0 '("one" "two" "three"))
    ⇒ "one"

(nth 1 '("one" "two" "three"))
    ⇒ "two"
```

--------------------------------

### Setup for count-words-in-defun

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/count_002dwords_002din_002ddefun.html

Initial setup code that moves to the beginning of the definition and initializes local variables for counting and boundary tracking.

```elisp
(beginning-of-defun)
(let ((count 0)
      (end (save-excursion (end-of-defun) (point))))
```

--------------------------------

### Install emacs2 keymap with install-keymap

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Miscellaneous.html

Installs the emacs2 keymap using install-keymap in a boot script as an alternative to loadkeys.

```shell
install-keymap emacs2

```

--------------------------------

### Modulo arithmetic examples with mod

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Determining-the-Element.html

Examples showing how the mod function returns the remainder of a division.

```elisp
(mod 12 4)
  ⇒ 0  ;; because there is no remainder
(mod 13 4)
  ⇒ 1
```

--------------------------------

### Conceptual if example

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/if-_0026-or.html

A conceptual example illustrating the logic of checking a condition and performing an action.

```elisp
(if (not (holding-on-to-guest))
    (find-and-take-arm-of-guest))
```

--------------------------------

### Start Emacs without loading init files

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Simple-Extension.html

Command line options to start Emacs without loading site or user initialization files, with specific evaluation.

```bash
emacs -q --no-site-file -eval '(blink-cursor-mode nil)'
```

--------------------------------

### Basic concat usage

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/kill_002dappend-function.html

A simple example demonstrating how the concat function joins two strings.

```elisp
(concat "abc" "def")
     ⇒ "abcdef"
```

--------------------------------

### Lisp List Syntax Example

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Lisp-Lists.html

A basic example of a Lisp list containing four flower names, demonstrating that lists can be formatted across multiple lines.

```lisp
'(rose
  violet
  daisy
  buttercup)
```

--------------------------------

### Initial while loop structure

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Loop-Example.html

Shows the start of a while loop testing the animals list.

```elisp
(while animals
       ...
```

--------------------------------

### Set start and goto-char expressions

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/fwd_002dpara-while.html

These two expressions set the variable start to the beginning of the matched text and move point to that location.

```emacs-lisp
(setq start (match-beginning 0))
(goto-char start)

```

--------------------------------

### Example calculation for next multiple

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Compute-a-Remainder.html

Evaluating the next multiple calculation with a height of 12.

```elisp
(* (1+ (/ 12 5)) 5)
```

--------------------------------

### Start building X-tic string

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/X-Axis-Tic-Marks.html

Begins constructing the X-tic string using concat and make-string.

```emacs-lisp
       (X-tic
        (concat
         (make-string

```

--------------------------------

### Compute remainders with %

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Compute-a-Remainder.html

Examples of using the % function to find the remainder of division.

```elisp
(% 7 5)

(% 10 5)
```

--------------------------------

### Execute square-each

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Every.html

Example usage of the square-each function showing the input list and the resulting squared list.

```elisp
(square-each '(1 2 3))
    ⇒ (1 4 9)
```

--------------------------------

### Test column-of-graph prototype

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Columns-of-a-graph.html

Example usage and expected output for the initial column-of-graph function.

```elisp
(column-of-graph 5 3)
```

```elisp
(" " " " "*" "*" "*")
```

--------------------------------

### Construct a list with cons

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/cons.html

This example demonstrates using cons to create a four-element list from an existing three-element list.

```elisp
(cons 'pine '(fir oak maple))
```

```elisp
(pine fir oak maple)
```

--------------------------------

### let expression structure in append-to-buffer

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/append_002dto_002dbuffer-body.html

An example showing the nested parentheses required for the let expression and its varlist.

```elisp
(let ((oldbuf (current-buffer)))
  ... )
```

--------------------------------

### Insert (debug) in code to start debugger

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/debug_002don_002dquit.html

Place (debug) in your code where you want the debugger to start. The example shows it inside a while loop before a deliberate error (1= number).

```emacs-lisp
(defun triangle-bugged (number)
  "Return sum of numbers 1 through NUMBER inclusive."
  (let ((total 0))
    (while (> number 0)
      (setq total (+ total number))
      (debug)                         ; Start debugger.
      (setq number (1= number)))      ; Error here.
    total))

```

--------------------------------

### Forward motion while loop in forward-paragraph

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/fwd_002dpara-while.html

This while loop searches forward for sp-parstart, moves point to the start of the match, and continues until the end of the paragraph. It uses match-beginning to get the start of the matched text.

```emacs-lisp
    (while (and (re-search-forward sp-parstart nil 1)
                (progn (setq start (match-beginning 0))
                       (goto-char start)
                       (not (eobp)))
                (progn (move-to-left-margin)
                       (not (looking-at parsep)))
                (or (not (looking-at parstart))
                    (and use-hard-newlines
                         (not (get-text-property (1- start) 'hard)))))
      (forward-char 1))

```

--------------------------------

### Call lengths-list-file on debug.el

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/lengths_002dlist_002dfile.html

Example invocation of lengths-list-file on the debug.el file in the default GNU Emacs 30.2 installation tree. Place cursor after the expression and type C-x C-e to evaluate.

```emacs-lisp
(lengths-list-file
 "/usr/local/share/emacs/30.2/lisp/emacs-lisp/debug.el")
```

--------------------------------

### Example: setq creates a two-element list

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/kill_002dnew-function.html

Sets example-list to a list of two strings. Evaluating this with C-x C-e and then evaluating example-list shows the list value.

```emacs-lisp
(setq example-list '("here is a clause" "another clause"))

```

```emacs-lisp
example-list
     ⇒ ("here is a clause" "another clause")

```

--------------------------------

### Global key binding for count-words-example

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Whitespace-Bug.html

A command to bind the count-words-example function to the C-c = key sequence.

```elisp
(keymap-global-set "C-c =" 'count-words-example)
```

--------------------------------

### Evaluated message expression example

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/multiply_002dby_002dseven-in-detail.html

An example of how the message expression is evaluated when a prefix argument of 5 is provided.

```elisp
(message "The result is %d" (* 7 5))
```

--------------------------------

### Sample mode line display

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Mode-Line.html

Shows the resulting mode line format after applying the custom configuration. It displays the file name, machine, directory, line number, mode, and buffer position.

```text
-:-- foo.texi   rattlesnake:/home/bob/  Line 1  (Texinfo Fill) Top

```

--------------------------------

### Start Emacs without initialization file

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Mode-Line.html

Use this command to launch a plain, default Emacs instance that does not load your ~/.emacs initialization file.

```bash
emacs -q
```

--------------------------------

### Documentation for goto-char

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/simplified_002dbeginning_002dof_002dbuffer.html

The documentation string for `goto-char` as shown by `describe-function`. It explains that the function sets point to a position, with the beginning of the buffer at `point-min` and the end at `point-max`.

```text
Set point to POSITION, a number or marker.
Beginning of buffer is position (point-min), end is (point-max).

```

--------------------------------

### defun example: multiply-by-seven

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/defun.html

Example function definition that multiplies its argument by 7. It is not interactive; see the section on Making a Function Interactive for that information.

```lisp
(defun multiply-by-seven (number)
  "Multiply NUMBER by seven."
  (* 7 number))

```

--------------------------------

### Implementation of count-words-example using let

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/recursive_002dcount_002dwords.html

The complete implementation of the interactive function, using a let expression to capture the result of the recursive call and display it to the user.

```elisp
(defun count-words-example (beginning end)
  "Print number of words in the region."
  (interactive "r")
```

```elisp
;;; 1. Set up appropriate conditions.
  (message "Counting words in region ... ")
  (save-excursion
    (goto-char beginning)
```

```elisp
;;; 2. Count the words.
    (let ((count (recursive-count-words end)))
```

```elisp
;;; 3. Send a message to the user.
      (cond ((zerop count)
             (message
              "The region does NOT have any words."))
            ((= 1 count)
             (message
              "The region has 1 word."))
            (t
             (message
              "The region has %d words." count))))))
```

--------------------------------

### Using let* for sequential variable binding

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Regexp-Review.html

Demonstrates let* which binds variables locally and allows subsequent bindings to reference previously bound variables.

```emacs-lisp
(let* ((foo 7)
       (bar (* 3 foo)))
  (message "`bar' is %d." bar))
     ⇒ ‘bar’ is 21.
```

--------------------------------

### Lisp String Atom Example

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Lisp-Atoms.html

An example of a list containing a string atom, which is treated as a single unit including its internal punctuation and spaces.

```Lisp
'(this list includes "text between quotation marks.")
```

--------------------------------

### Construct a list using dotimes

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/dotimes.html

This example binds the numbers 0, 1, and 2 to the variable 'number' and constructs a list of these three numbers.

```elisp
(let (value)      ; otherwise a value is a void variable
  (dotimes (number 3)
    (setq value (cons number value)))
  value)

⇒ (2 1 0)
```

--------------------------------

### Example list argument for insert-rectangle

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Columns-of-a-graph.html

An example of a list argument passed to insert-rectangle to represent a column of height 3 in a graph with a maximum height of 5.

```elisp
(" " " " "*" "*" "*")
```

--------------------------------

### List Construction with cons

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/cons-_0026-search_002dfwd-Review.html

Shows how to prepend an element to the front of an existing list.

```elisp
(cons 1 '(2 3 4))
     ⇒ (1 2 3 4)
```

--------------------------------

### Example invocations of triangle function

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Inc-Example-altogether.html

Two example calls to the triangle function: (triangle 4) and (triangle 7). The first returns 10 and the second returns 28.

```emacs-lisp
(triangle 4)

```

```emacs-lisp
(triangle 7)

```

--------------------------------

### First version of count-words-example (with bugs)

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Design-count_002dwords_002dexample.html

This is the initial implementation of the count-words-example function. It uses interactive "r" to get the region, and prints a message. The function is known to have bugs and does not work in all circumstances.

```emacs-lisp
;;; First version; has bugs!
(defun count-words-example (beginning end)
  "Print number of words in the region.
Words are defined as at least one word-constituent
character followed by at least one character that
is not a word-constituent.  The buffer's syntax
table determines which characters these are."
  (interactive "r")
  (message "Counting words in region ... ")


```

```emacs-lisp


```

```emacs-lisp
;;; 1. Set up appropriate conditions.
  (save-excursion
    (goto-char beginning)
    (let ((count 0))


```

```emacs-lisp


```

```emacs-lisp
;;; 2. Run the while loop.
      (while (< (point) end)
        (re-search-forward "\\w+\\W*")
        (setq count (1+ count)))


```

```emacs-lisp


```

```emacs-lisp
;;; 3. Send a message to the user.
      (cond ((zerop count)
             (message
              "The region does NOT have any words."))
            ((= 1 count)
             (message
              "The region has 1 word."))
            (t
             (message
              "The region has %d words." count))))))

```

--------------------------------

### Call add-elements with example list

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Accumulate.html

Invokes add-elements with the list (1 2 3 4) and shows the result 10.

```emacs-lisp
(add-elements '(1 2 3 4))
    ⇒ 10

```

--------------------------------

### Example output for print-graph

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Test-print_002dgraph.html

The visual output generated by the print-graph function.

```text
10 -


         *
        **   *
 5 -   ****  *
       **** ***
     * *********
     ************
 1 - *************

     |   |    |    |
     1   5   10   15
```

--------------------------------

### Evaluate multiply-by-seven

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Effect-of-installation.html

Evaluates the multiply-by-seven function with the argument 3 to verify its installation.

```elisp
(multiply-by-seven 3)
```

--------------------------------

### Edebug result display

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/edebug.html

Example of a value displayed in the echo area during debugging.

```text
Result: 3 (#o3, #x3, ?\C-c)
```

--------------------------------

### Updating set-buffer to use bound variables

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/append-save_002dexcursion.html

Demonstrates the transition from using a function call directly to using a variable bound in a let* expression.

```elisp
(set-buffer (get-buffer-create buffer))
```

```elisp
(set-buffer append-to)
```

--------------------------------

### Example of a nested Lisp list

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Numbers-Lists.html

A list containing words and an interior list.

```lisp
'(this list has (a list inside of it))
```

--------------------------------

### Evaluate addition

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Making-Errors.html

An example of a successful evaluation where the symbol '+' has a defined function.

```elisp
(+ 2 2)
```

--------------------------------

### Evaluate functions with three arguments

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Variable-Number-of-Arguments.html

Demonstrates evaluating the addition and multiplication functions with three arguments.

```elisp
(+ 3 4 5) ⇒ 12

(* 3 4 5) ⇒ 60
```

--------------------------------

### Example of a text storage list

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/Storing-Text.html

A representation of how successive pieces of text are stored in a list.

```elisp
("a piece of text" "previous piece")
```

--------------------------------

### Display a message with multiple arguments

Source: https://www.gnu.org/software/emacs/manual/html_node/eintr/message.html

Demonstrates using both %d and %s placeholders with multiple arguments.

```elisp
(message "There are %d %s in the office!"
         (- fill-column 14) "pink elephants")
```
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