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@ -18,51 +18,52 @@ enlightenment.
A list in Lisp is composed of `cons` cells which have two fields: the contained value of the cell known as `car` and a pointer to the
next cell known as `cdr`. To mark the end of a list, a special sentinel value, `NIL` is used, which represents an empty list.
Here's cons cell:
```
A cons cell:
+---+---+
| O | O-|----> cdr
+---+---+
|
`'´
car
```
To create a cell, `cons` is used:
(cons 1 2) ; 1 and 2 are the car and cdr respectively
(car (cons 1 2)) ; ==> 1
(cdr (cons 1 2)) ; ==> 2
Also some Lisps accept the "dotted pair" notation as a shorthand:
(1 . 2)
And a list, composed of linked cons cells where `NIL` is the end sentinel:
To create a cell, the builtin function `cons` is used:
```lisp
(cons 1 2) ; 1 and 2 are the car and cdr respectively
(car (cons 1 2)) ; ==> 1
(cdr (cons 1 2)) ; ==> 2
;; Also some Lisps accept the "dotted pair" notation as a shorthand:
(1 . 2)
```
And here's a list:
```
cdr cdr cdr cdr
+---+---+ +---+---+ +---+---+ +---+---+
| O | O-|---->| O | O-|---->| O | O-|---->| o | O-|----> NIL
+-|-+---+ +---+---+ +---+---+ +---+---+
car | car | car | car |
`'´ `'´ `'´ `'´
20 "Lisp" (1 2) 39
20 "Lisp" (1 2) 39
```
Using cons:
(cons 20 (cons "Lisp" (cons '(1 2) (cons 39 '()))))
In cons dotted pair notation:
(20 . ("Lisp" . ('(1 2) . (39 . NIL))))
Using quote:
'(20 "Lisp" '(1 2) 39)
Creating lists:
```lisp
;; Using cons:
(cons 20 (cons "Lisp" (cons '(1 2) (cons 39 '()))))
;; In cons dotted pair notation:
(20 . ("Lisp" . ('(1 2) . (39 . NIL))))
;; Using quote:
'(20 "Lisp" '(1 2) 39)
;; Most Lisps provide a `list` function:
(list 20 "Lisp" '(1 2) 39)
```
## Lisp languages in use
- [Scheme](scheme.md): created by the hackers Guy Steele and Gerald Sussman in 1975 at the MIT. Has multiple implementations, Chez Scheme,
Chicken Scheme, MIT/GNU Scheme, etc.
- [Scheme](scheme.md): created by the hackers Guy Steele and Gerald Sussman in 1975 at the MIT.
- [Common Lisp](common_lisp.md): Big for Lisp standards (still better and smaller than "modern" languages), is also the most used Lisp today.
The main implementation is SBCL, a public domain JIT compiler.
- GNU Guille
- Clojure: based in the [JVM](jvm.md) (Java Virtual Machine), does not have `cons`, `car` or `cdr`.
- ...