rosprolog is a bidirectional interface between SWI Prolog and ROS, and a wrapper around roscpp. It provides predicates that enable Prolog programmers to quickly interface with ROS subsystems, and to maintain dependencies to other ROS packages. It further implements a ROS node that enables other ROS components to query a Prolog engine.

rosprolog packages are normal ROS packages that, in addition, contain some special files and folders. This common structure allows to automatically load the package and all its dependencies.

my_package
|- package.xml
|- CMakeLists.txt
|- rdf
   |- my_ontology.rdf
|- src
   |- __init__.pl
   |- my_module.pl
   |- my_module.plt

To run rosprolog, use:

rosrun rosprolog rosprolog

To start a prolog package within rosprolog (incl. calling its init.pl file and all init.pl of referenced packages), use:

rosrun rosprolog rosprolog <pkgname>

The interactive Prolog shell is good for exploring KnowRob, visualizing knowledge, developing new functions and debugging Prolog code.

However, if you would like to use KnowRob in your robot's control program, you need a way to send queries from your program. This functionality is provided by the rosprolog package. It provides a service that exposes a Prolog shell via ROS. You can run the rosprolog service using a launch file such as the following

<launch>
  <arg name="initial_package" default="knowrob_common" />
  <arg name="initial_goal" default="knowrob_common" />
  <arg name="num_pl_threads" default="2" />
  <arg name="num_ros_threads" default="4" />
  
  <param name="initial_package" type="string" value="$(arg initial_package)" />
  <param name="initial_goal" type="string" value="$(arg initial_goal)" />
  
  <param name="num_pl_threads" type="int" value="$(arg num_pl_threads)" />
  <param name="num_ros_threads" type="int" value="$(arg num_ros_threads)" />
  
  <node name="rosprolog" pkg="rosprolog" type="rosprolog_node" cwd="node" output="screen" />
</launch>

The rosprolog_node reads some optional ROS parameters for the initial package to be loaded (that you also give as argument when starting rosprolog) and a command to be executed at startup.

You can get an interactive console for a running rosprolog node with

rosrun rosprolog rosprolog_commandline.py

Unit testing in Prolog is done via the library plunit. rosprolog defines a CMake macro that allows adding plunit testcases to the rostest suite.

catkin_add_plunit(knowrob/comp_spatial)

Test files should by placed next to the source file that is tested but with a plt file extension. The testcase must be named exactly like the path to the module, i.e., in above case "knowrob/comp_spatial".

Another way to run the tests is by invoking the rosprolog-test script:

rosrun rosprolog rosprolog-test comp_spatial:"knowrob/comp_spatial"