.LISP File Format

Introduction

Common Lisp is the standardised dialect of Lisp, the family of languages begun by John McCarthy in 1958. It was published as ANSI standard X3.226 in 1994 and has several independent implementations, among them SBCL.

Source files are named .lisp, .lsp or .cl. A project is described by an .asd file for the ASDF build system, and compilers save their output as a fasl file.

Two of these extensions have other uses. .lsp is also used for AutoLISP routines in AutoCAD, a separate dialect, and .cl is also used for OpenCL C, the language of programs for graphics cards and other accelerators.

Structure

A Lisp file is plain text made of forms, which are parenthesised lists or single values, read and evaluated one after another. The first word in a list is the operator. ; starts a comment to the end of the line and #| … |# marks a block comment. The reader converts unquoted symbols to upper case by default, so greet and GREET are the same symbol.

Files usually begin by defining or selecting a package with defpackage and in-package. Named definitions follow, with defun for functions, defvar and defparameter for variables, defmacro for macros and defclass for classes. The loop and format facilities are little languages of their own. Reader macros, written with #, change how the text that follows is read.

(defpackage :greeting
  (:use :common-lisp))

(in-package :greeting)

;; Print a greeting, one line per name.
(defun greet (names)
  "Print a greeting for each of NAMES."
  (dolist (name names)
    (format t "Hello, ~a~%" name)))

(greet '("Ada" "Grace"))

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