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# Lisp Cheatsheet Lisp is a family of programming languages that are based on the lambda calculus and characterized by their use of parentheses for code blocks. Lisp is a powerful language with a simple syntax, making it a popular choice for artificial intelligence, data processing, and web development. ## Unique Features - Code as data - Macros - Dynamic typing - Recursion - Functional programming - Interactive development ## Variables Variables in Lisp are declared using the `defvar` or `setq` function. Lisp supports dynamic typing, so you don't need to specify the type of the variable.
(defvar name "John")
(setq age 30)
(setq pi 3.14)
## Functions Functions in Lisp are declared using the `defun` function followed by the function name and parameters. Lisp supports lambda expressions, which are anonymous functions that can be assigned to variables and passed as arguments to other functions.
(defun greet (name)
(format t "Hello, ~a!" name))
(greet "John")
(setq add (lambda (a b)
(+ a b)))
(print (funcall add 2 3))
## Loops Lisp supports `do`, `dotimes`, and `dolist` loops, as well as recursion.
(setq numbers '(1 2 3 4 5))
(dolist (number numbers)
(print number))
(dotimes (i 5)
(print i))
(defun countdown (n)
(when (> n 0)
(print n)
(countdown (- n 1))))
(countdown 5)
## Conditionals Lisp supports `if`, `when`, and `unless` statements, as well as the `cond` control structure.
(setq age 30)
(if (< age 18)
(print "You are too young to vote.")
(if (< age 21)
(print "You can vote, but not drink.")
(print "You can vote and drink.")))
(setq result (if (>= age 18) "You are an adult" "You are not an adult"))
(print result)
## File Manipulation Lisp provides several ways to read and write files. You can use the `with-open-file` macro to create, read, write, and delete files.
(with-open-file (file "example.txt" :direction :output)
(write-line "Hello, world!" file))
(with-open-file (file "example.txt" :direction :input)
(let ((content (read-line file)))
(print content)))
(delete-file "example.txt")
## Resources - [Common Lisp HyperSpec](http://www.lispworks.com/documentation/HyperSpec/Front/index.htm) - [Practical Common Lisp](http://www.gigamonkeys.com/book/) - [Lisp Koans](https://github.com/google/lisp-koans) - [Lisp REPL](https://lispwebtales.gitlab.io/repl/)