Common Lisp: A Practical Introduction

Background
- Key Implementations
Getting Started
Macros
CLOS (Common Lisp Object System)
Resources

Background

Common Lisp is a dialect of Lisp standardized by ANSI in 1994. It combines functional, procedural, and object-oriented paradigms with a powerful macro system that enables compile-time code generation.

Key Implementations

Implementation	Description
SBCL	Steel Bank Common Lisp (fast)
CCL	Clozure Common Lisp
ECL	Embeddable Common Lisp
ABCL	Armed Bear (JVM-based)

Getting Started

;; Install SBCL and Quicklisp
;; (load "~/quicklisp/setup.lisp")

;; Basic function definition
(defun factorial (n)
  "Calculate factorial of N."
  (if (<= n 1)
      1
      (* n (factorial (1- n)))))

(factorial 5)  ; => 120

;; Higher-order functions
(mapcar #'1+ '(1 2 3 4 5))  ; => (2 3 4 5 6)

(reduce #'+ '(1 2 3 4 5))   ; => 15

Macros

Macros are compile-time code transformations:

;; Define a simple macro
(defmacro when-let ((var expr) &body body)
  "Bind VAR to EXPR and execute BODY if non-nil."
  `(let ((,var ,expr))
     (when ,var
       ,@body)))

;; Usage
(when-let (user (find-user "alice"))
  (format t "Found: ~a~%" user))

CLOS (Common Lisp Object System)

;; Define a class
(defclass person ()
  ((name :initarg :name :accessor person-name)
   (email :initarg :email :accessor person-email)))

;; Define a method
(defmethod greet ((p person))
  (format nil "Hello, ~a!" (person-name p)))

;; Create an instance
(let ((alice (make-instance 'person :name "Alice" :email "alice@example.com")))
  (greet alice))  ; => "Hello, Alice!"