[CMake] CMake and Lua

[Peter Kümmel]

Hi Ken,

this is a reply to your email on the Lua list:
http://marc.info/?l=lua-l&m=120275861422593&w=2

It is nice to see that there is interest in Lua as
alternative scripting language. Since I've discovered
Lua I thought it would be a nice drop-in for the
actual CMake macro language.


Here I wanna post some ideas about the general architecture.

In principle CMake implements two thing,
     - a scripting language,
     - and a make/build-file generator.

As I understand it, these two things are currently
mixed up in CMakeLib: all commands parse the arguments
(scripting functionality) and then call the generator
function with the found arguments, for instance
   this->Makefile->AddSubDirectory(..

This makes it hard to introduce a new scripting language,
if it should not only be a wrapper of the current cmake
commands.
Isn't this your ansatz in your Lua experiment?
http://www.cmake.org/Wiki/CMake:Experiments_With_Lua
http://www.assembla.com/wiki/show/CMakeLua


I would choose a different way:
First I would split the current CMakeLib into two libs,
one which implements the macro language, and the other
which implements the generator stuff only, nothing knowing
about any scripting/macro language.

Then a binding of the macro language to the generator lib
gives you a backward compatible CMake version.

If only this is done, nothing is won. But with this layout,
it would be much easer to use other scripting languages.
With this architecture you don't have to definitely exclude all
other scripting languages when choosing Lua as additional new
language.

Kitware could officially support Lua and KitwareScripting, the
old macro language, and at the same time provide a well proven
cross-plattform build-file generator library which could easily
be used by other scripting languages (imported as an external module).

On the long run this gives you a much greater user/developer base,
and gives the build-file generator library the chance to become
the standard in cross-platform builds systems.


Some scenarios I could imagine:

- if there is a binding done with
   http://www.swig.org/
   CMake could be used by all popular scripting languages
- maybe Trolltech finds it convenient to replace their
   proprietary build-file generators, and join forces with
   Kitware. Then it is possible that CMake is sometimes part
   of Nokia/Symbian projects' build process
- someone binds CMake to autotools/m4 (don't know if this is possible)
- a PHP binding to manage the build process with a browser,
   don't know why someone would do this ;)
- with a bjam binding it finds its way into boost
   (What's the current status of boost's cmake branch?)
- "CMake everywhere" in analogy to the slogan of TT
- SCons uses CMake to generate build-files as alternative to
   their build files
- with Kross the scripting language becomes transparent
   http://kross.dipe.org/


More scenarios or comments are welcome.


Best regards,
Peter Kümmel