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This repository contains the open source version of the SHOP3 Hierarchical Task Network (HTN) AI planner.

Version 3.8.1 Release (2023-01-25)

In support of work I (RPG) have done to add Monte Carlo Tree Search to SHOP3, I have made a number of minor improvements, bugfixes, etc. These changes are of general interest/value, so they are now released as version 3.8.1 of SHOP. Descriptions of the changes may be found in the ChangeLog.


Mozilla Public License

Installation Instructions

Common Lisp

SHOP3 is written in Common Lisp (CL), and requires a CL implementation to run. We recommend one of the following implementations:

  • SBCL: Steel Bank Common Lisp. Available in packages on Ubuntu Linux and Mac Homebrew. Also available from
  • CCL: Clozure Common Lisp. Available from
  • ACL: Allegro Common Lisp: Available from Unlike the previous two implementations, this is a commercial software product.
  • LispWorks: Recently we have been given a license to test SHOP3 on LispWorks, and have verified that the SHOP3 test suite passes on LW. Like Allegro, LispWorks is a commercial lisp implementation.

We regularly test SHOP3 on all of these lisp implementations, using an exhaustive test suite. There are at least a handful of other CL implementations, both open source and commercial, but we have not tested them with SHOP3. Attempts to run SHOP3 on ECL, ABCL, and clisp have not been successful. Patches to make SHOP3 work with other implementations are welcomed, but we have no plans to add support to any others ourselves.

Note that we have not tested SHOP3 on the free versions of ACL or LispWorks, and we do not expect it to work well on these platforms because of their resource limitations. For hobbyist projects, we suggest SBCL or CCL instead.

Obtaining the code

Clone this repository and then initialize and populate the submodules.

git clone

See the two installation options below to see whether you need to supply the --recurse-submodules option when cloning.

Once you have done that, you can get SHOP3 started either using Quicklisp (probably easiest) or by configuring ASDF (the Common Lisp build manager) yourself. See below.

Option 1: Quicklisp

Probably the easiest way to work with SHOP3 will be to use it in conjunction with Quicklisp. Quicklisp is a package manager for CL libraries, and will be the easiest way to get the libraries that SHOP3 depends on.

If you wish to use Quicklisp, follow the installation instructions for quicklisp at the above site. Now you have two choices: you can install SHOP3 through Quicklisp, or you can check out SHOP3 from here (GitHub) and use Quicklisp only for the required dependencies.

The Easy way -- do everything with Quicklisp

  1. Start CL
  2. Inside CL, enable Quicklisp
  3. Enter (ql:quickload "shop3") into the CL REPL.

With your own copy of SHOP3

This installation method is best for someone who is interested in developing new HTN planning capabilities with SHOP and will want to be modifying the source of the planning system. If you would just like to develop planning domains and problems, then the simpler, all-Quicklisp method is probably better for you. You can always check out a copy of the repo later if you want.

  1. Clone the SHOP3 repository into the local-projects subdirectory of your

Quicklisp install directory (see the Quicklisp docs). 2. Start CL 3. Inside CL, enable Quicklisp 4. Enter (ql:quickload "shop3") into the CL REPL.

Quicklisp contains all of the dependencies that SHOP3 requires except the "pddl-utils" system. This system is only used in the tests, or for some optional functionality. If you wish to have this subsystem, you can either;

  1. populate the git submodules -- or just the pddl-tools one -- in the SHOP3 git

repository, OR 2. Clone the pddl-tools repository into local-projects, as well, and do not bother with the git submodules.

Option 2: Without Quicklisp

The SHOP3 repository has links to all of the libraries it requires in its git submodules. If Quicklisp is not the right approach for you, you must use git commands to populate SHOP3's submodules (if you like, you may clone with the --recurse-submodules option), and then:

  1. Start CL
  2. Load the ASDF CL build system by doing (require :asdf) in the CL REPL.
  3. Tell ASDF where to find SHOP3:
             '(:source-registry (:tree SHOP3-DIRECTORY) :inherit-configuration))
    Fill in the name of the directory of your cloned repository for SHOP3-DIRECTORY.
  4. Enter (asdf:load-system "shop3") into the CL REPL.

Once started

We suggest that you interact with SHOP3 through the shop-user package in the REPL, for exploratory work. If you wish to develop a more substantial planning application, we recommend starting a new system in a dedicated package that will :use-package shop3.

The best environment for working with CL for any purpose, including SHOP3 planning, is through the Superior Lisp Interaction Mode for Emacs, or SLIME or its fork, SLY. Both of these are available for installation through MELPA using the Emacs package manager.

If you use Allegro Common Lisp, Franz have their own Emacs Lisp Interface (ELI) as a possible alternative.

Allegro, CCL, and Lispworks each have some sort of GUI/IDE, as well.

Using SHOP3

See the user manual in the docs directory of the repository. Building the manual requires having texinfo, and SBCL installed, and benefits from having tex/latex installed. To build, change to the docs directory and do make html if you have only makeinfo installed, or just make if you have tex/latex, as well. This will produce the manual in HTML, Emacs info, and PDF formats.


If you have questions, please post them using the Discussions link.

Now that GitHub has added discussions, we would prefer to keep issues for actual bug reports.

Citing SHOP3

The best way to cite SHOP3 is to cite the paper "Hierarchical Task Network Planning in Common Lisp: the case of SHOP3": Goldman, R.P. and Kuter, U. (2019) ‘Hierarchical Task Network Planning in Common Lisp: the case of SHOP3’, in Proceedings of the 12th European Lisp Symposium. European Lisp Symposium, Genova, Italy.


  title = {Hierarchical {{Task Network Planning}} in {{Common Lisp}}: The Case of {{SHOP3}}},
  booktitle = {Proceedings of the 12th {{European Lisp Symposium}}},
  author = {Goldman, Robert P and Kuter, Ugur},
  year = {2019},
  month = apr,
  address = {{Genova, Italy}}

Dependencies (5)

  • alexandria
  • cl-dot
  • fiveam-asdf
  • iterate
  • trivial-garbage

Dependents (0)

    • GitHub
    • Quicklisp