clips_vendor

Wrapper around clips (https://clipsrules.net/) for usage with ROS 2. Replaces the make-based original build system by cmake and builds dynamic libraries for flexible usage.

Contains core implementation, clipsjni applications and demos as well as the given examples from the svn source repository (https://svn.code.sf.net/p/clipsrules/code).

Note that clips can be both compiled with c and c++. Here, the main application and library libclips.so is built using c++. A c shared library libclips_c.so is also provided (and used by the clipsjni applications). Furthermore, a namespaced version libclips_ns.so is supplied, which wraps the original files with namespace clips {} to minimize conflicts with other libraries and projects.

As clips is written as as a C project there are no namespaces and a lot of preprocessor macros involved, which requires some careful considerations. Make sure to read the Known Issues to avoid some of the related pitfalls.

Usage

in CMake:

find_package(clips_vendor)
find_package(clips)

...

target_link_libraries(<target> PUBLIC Clips::libclips)      # when using c++ compiled library
target_link_libraries(<target> PUBLIC ClipsC::libclips_c)   # when using c compiled library
target_link_libraries(<target> PUBLIC ClipsNS::libclips_ns) # wen using namespaced c++ library

in C++:

#include<clips/clips.h>    // when using libclips

extern C {
  #include<clips/clips.h>    // when using libclips_c
}

#include<clips_ns/clips.h> // when using libclips_ns

Known Issues

Clashes with other Libraries

As libclips and libclips_c contain unnamespaced definitions of structs and functions, it is recommended to use libclips_ns instead, to prevent accidental clashes with other libraries.

Regardless of the chosen clips library, inside of CLIPS headers there are a #define macros that might interfere with other libraries. For example, LHS and RHS macros interfere with template identifiers in boost/function_types/property_tags.hpp.

In these cases, undefine the macros after including the clips.h header.

Mixing of Macros and Enums in libclips_ns

Another issue is the mixing of typedef and enums when working with the namespaced version of the library. Looking at this snippet from constant.h:

typedef enum
  {
   FLOAT_BIT = (1 << 0),
   INTEGER_BIT = (1 << 1),
   // ...
  } CLIPSType;

#define NUMBER_BITS (INTEGER_BIT | FLOAT_BIT)

With namespace wrapping, the "unscoped" enum requires the usage of a namespace to reference the values, e.g., clips::FLOAT_BIT. However, the macro NUMBER_BITS expands to just (INTEGER_BIT | FLOAT_BIT) which is only valid when the expansion is wrapped in the namespace

In this scenario it is necessary to use using namespace clips; before using the NUMBER_BITS. In particular, clips::NUMBER_BITS is not valid, neither is just using NUMBER_BITS without having declared the usage of namespace clips.