Creating a CRAM package

Description: In this tutorial you will set up a ROS package to use the CRAM plan language within the Lisp REPL. You can find the code resulting from the beginner tutorials on GitHub..

Next Tutorial: Controlling turtlesim from CRAM

Creating a ROS package

First we need to create a ROS package that depends on cram_language. On the ROS website there are two tutorials on creating a package: Package creation and Package creation by hand (it is recommended that you work with catkin and not legacy rosbuild).

In the src subdirectory of your ROS workspace execute the following command:

$ catkin_create_pkg cram_beginner_tutorial cram_language 

Setting up the Lisp infrastructure

Setting up the Common Lisp part is a little bit more work. First, we need to create a Lisp 'project file', i.e. an ASDF system. After that we will need to create a Common Lisp package (i.e. the equivalent of C++ namespaces). You can learn roslisp in more detail through roslisp tutorials

Creating an ASDF system

Switch into the root directory of the cram_beginner_tutorial package and create a file cram-beginner-tutorial.asd. You shouldn't use underscores but dashes in .asd file names. The reason is that the system that is defined in the .asd file should be named like the file itself and in Lisp it is very uncommon to use underscores in general.

Put the following content into cram-beginner-tutorial.asd:

(defsystem cram-beginner-tutorial
  :depends-on (cram-language)
  ((:module "src"
            ((:file "package")
             (:file "control-turtlesim" :depends-on ("package"))))))

The first line defines the name of the system. Then we specify the dependencies of the system, i.e. other systems that need to be loaded before we load our system.

Finally, we define the components of the system. A component is a sort of sub-system and might be either a module (i.e. a sub-directory) or a file. ASDF knows some more component types but they are not relevant for us most of the time. We define that the system knows a sub-directory src. Further, we define that this module contains two components, one file for the package definition package.lisp and one with the actual tutorial code control-turtlesim.lisp that has exactly one dependency - the component package. We will create these two source files next. Dependencies inside the system can be any component that is known in the current scope. That means that a component can only depend on those components that are defined in the same parent component. Please note that the file extension must be left out when defining files.

Creating the Lisp Package

Lisp packages are the equivalent to C++ namespaces or Python modules. Lisp packages cannot be hierarchical. Through Lisp packages we can define which other packages should be used, i.e. which symbols should be accessible without a package prefix. Further, we can define which symbols should be exported from the package.

Create a sub-directory src in your package. Then create the file package.lisp and put the following code into it:

(defpackage :cram-beginner-tutorial
  (:nicknames :tut)
  (:use :cpl))

We define a package with the name cram-beginner-tutorial. Packages in Common Lisp can have an arbitrary number of nicknames. In our case we nickname cram-beginner-tutorial as tut. Finally, we define that the package uses another package cpl which is a nickname of the package cram-language from the metapackage cram_core.

Exporting the ASDF system to ROS

To actually load the ASDF system, all files referenced in the system definition must be present and we are missing the file control-turtlesim.lisp in src, so create it with the following content:

(in-package :tut)

This just selects the namespace of the file by the nickname :tut we defined in package.lisp. We will fill it with more content in the next tutorial.

Now we are ready to compile and load our new system. Launch the Lisp REPL ($ roslisp_repl, if you already have a REPL running, keep in mind that you need to restart it whenever a new ROS package is added to the workspace). Then load your newly created system by typing:

CL-USER> (ros-load:load-system "cram_beginner_tutorial" :cram-beginner-tutorial)

This loads the cram-beginner-tutorial of the package cram_beginner_tutorial. Test it by evaluating

CL-USER> (in-package :tut)


Now that we have created our first CRAM package, let's try controlling the ROS turtlesim from it…

Controlling turtlesim from CRAM