The Common Lisp Cookbook – Getting started

Easy steps to install a development environment and start a project.

Want a 2-clicks install ? Then get Portacle, a portable and multiplatform Common Lisp environment. It ships Emacs25, SBCL (the implementation), Quicklisp (package manager), Slime (IDE) and Git. It’s the most straightforward way to get going !

Install an implementation

With your package manager


apt-get install sbcl

Common Lisp has been standardized via an ANSI document, so it can be implemented in different ways: see Wikipedia’s list of implementations.

The following are packaged for Debian and probably for your distro:

In doubt, just get SBCL.

See also

and this Debian package for Clozure CL.

With Roswell

Roswell is:

  • an implementation manager: it makes it easy to install a Common Lisp implementation (ros install ecl), an exact version of an implementation (ros install sbcl/1.2.0), to change the default one being used (ros use ecl),
  • a scripting environment (helps to run Lisp from the shell, to get the command line arguments,…),
  • a script installer,
  • a testing environment (to run tests, including on popular Continuous Integration platforms),
  • a building utility (to build images and executables in a portable way).

You’ll several ways of installation on its wiki (Debian package, Windows installer, Brew/Linux Brew,…).

Start a REPL

Just launch the implementation executable on the command line to enter the REPL (Read Eval Print Loop), i.e. the interactive interpreter.

Quit with (quit) or ctr-d (on some implementations).

Here is a sample session:

user@debian:~$ sbcl
This is SBCL 1.3.14.debian, an implementation of ANSI Common Lisp.
More information about SBCL is available at <>.

SBCL is free software, provided as is, with absolutely no warranty.
It is mostly in the public domain; some portions are provided under
BSD-style licenses.  See the CREDITS and COPYING files in the
distribution for more information.
* (+ 1 2)

* (quit)

You can slightly enhance the REPL (the arrow keys do not work, it has no history,…) with rlwrap:

apt-get install rlwrap


rlwrap sbcl

But we’ll setup our editor to offer a better experience instead of working in this REPL. See editor-support.


Common Lisp has hundreds of libraries available under a free software licence. See:

  • Quickdocs - the library documentation hosting for CL.
  • the Awesome-cl list, a curated list of libraries.
  • Cliki, the Common Lisp wiki.

Some terminology

  • In the Common Lisp world, a package is a way of grouping symbols together and of providing encapsulation. It is similar to a C++ namespace, a Python module or a Java package.

  • A system is a collection of CL source files bundled with an .asd file which tells how to compile and load them. There is often a one-to-one relationship between systems and packages, but this is in no way mandatory. A system may declare a dependency on other systems. Systems are managed by ASDF (Another System Definition Facility), which offers functionalities similar to those of make and, and has become a de facto standard.

  • A Common Lisp library or project typically consists of one or several ASDF systems (and is distributed as one Quicklisp project).

Install Quicklisp

Quicklisp is more than a package manager, it is also a central repository (a dist) that ensures that all libraries build together.

It provides its own dist but it is also possible to build our own.

To install it, we can either:

1- run this command, anywhere:

curl -O

and enter a Lisp REPL and load this file:

sbcl --load quicklisp.lisp


2- install the Debian package:

apt-get install cl-quicklisp

and load it, from a REPL:

(load "/usr/share/cl-quicklisp/quicklisp.lisp")

Then, in both cases, still from the REPL:


This will create the ~/quicklisp/ directory, where Quicklisp will maintain its state and downloaded projects.

If you want Quicklisp to always be loaded in your Lisp sessions, run (ql:add-to-init-file): this adds the right stuff to the init file of your CL implementation. Otherwise, you have to run (load "~/quicklisp/setup.lisp") in every session if you want to use Quicklisp or any of the libraries installed through it.

It adds the following in your (for example) ~/.sbclrc:

  (let ((quicklisp-init (merge-pathnames "quicklisp/setup.lisp"
    (when (probe-file quicklisp-init)
      (load quicklisp-init)))

Install libraries

In the REPL:

(ql:quickload "package-name")

and voilà. See Quicklisp’s documentation for more commands.

Note also that dozens of Common Lisp libraries are packaged in Debian. The package names usually begin with the cl- prefix (use apt-cache search --names-only "^cl-.*" to list them all).

For example, in order to use the CL-PPCRE library (for regular expressions), one should first install the cl-ppcre package.

Then, in SBCL and ECL, it can be used with:

(require "asdf")
(require "cl-ppcre")
(cl-ppcre:regex-replace "fo+" "foo bar" "frob")

See more:

Advanced dependencies management

Note that you don’t need to know that to get started.

Quicklisp installs the libraries into ~/quicklisp/local-projects/. A library installed here is automatically available for every project.

Providing our own version of a library. Cloning projects.

Given the property above, we can clone any library into the local-projects directory and it will be found by quicklisp and available right-away:

(ql:quickload "package")

How to work with local versions of libraries

If we need libraries to be installed locally, for only one project, or in order to easily ship a list of dependencies with an application, we can use Qlot.

Quicklisp also provides Quicklisp bundles. They are self-contained sets of systems that are exported from Quicklisp and loadable without involving Quicklisp.

At last, there’s Quicklisp controller to help us build dists.

Working with projects

Now that we have Quicklisp and our editor ready, we can start writing Lisp code in a file and interacting with the REPL.

But what if we want to work with an existing project or create a new one, how do we proceed, what’s the right sequence of defpackage, what to put in the .asd file, how to load the project into the REPL ?

Creating a new project

Some project builders help to scaffold the project structure. We like cl-project that also sets up a tests skeleton.

In short:

(ql:quickload "cl-project")
(cl-project:make-project #P"./path-to-project/root/")

it will create a directory structure like this:

|-- my-project.asd
|-- my-project-test.asd
|-- README.markdown
|-- src
|   `-- my-project.lisp
`-- tests
    `-- my-project.lisp

Where my-project.asd ressembles this:

(defsystem "my-project"
  :version "0.1.0"
  :author ""
  :license ""
  :depends-on ()  ;; <== list of Quicklisp dependencies
  :components ((:module "src"
                ((:file "my-project"))))
  :description ""
     (subpathname *load-pathname* "README.markdown"))
  :in-order-to ((test-op (test-op "my-project-test"))))

and src/my-project.lisp this:

(defpackage footest
  (:use :cl))
(in-package :footest)

How to load an existing project

You have created a new project, or you have an existing one, and you want to work with it on the REPL, but Quicklisp doesn’t know it. How can you do ?

Well first, if you create it or clone it into ~/quicklisp/local-projects, you’ll be able to (ql:quickload …) it with no further ado.

Otherwise you’ll need to compile and load its system definition (.asd) first. In Slime, type C-c C-k (slime-compile-and-load-file) in the .asd, then you can (ql:quickload …) it.

Usually you want to “enter” the system in the REPL at this stage:

(use-package :my-project)

Lastly, you can compile or eval the sources (my-project.lisp) with C-c C-k or C-c C-c (slime-compile-defun) in a form, and see its result in the REPL.

Another solution is to use ASDF’s list of known projects:

(pushnew "~/path-to-project/root/" asdf:*central-registry* :test #'equal)

and since ASDF is integrated into Quicklisp, we can quickload our project.

Happy hacking !

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