What is Kollos?
Kollos is the next phase of Marpa. Today, Marpa's main implementation consist of these pieces:
a C library, called Libmarpa, which implements the core parse engine. It's very low-level -- for example, there are no strings. Rules, symbols, error messages, etc. are all integers.
a Perl/XS wrapper, also in C, which provides the necessary upper layer for Libmarpa and contains most of the SLIF logic.
pure Perl logic, which combined with the previous two becomes Marpa::R2, a Perl module
Kollos will replace the Perl/XS wrapper with Lua. In the process Lua will become the language for Marpa's semantics -- that is, you'll be able to specify custom logic in Lua. Lua is extremely minimal and lightweight, and is perfect for this purpose.
Where does the name "Kollos" come from?
This thing you call language though, most remarkable. You depend on it for so very much. But is any one of you really its master? -- Kollos
The name of this project is that of a Star Trek character, Kollos. He's the Medusan ambassador in Episode 5 of Season 3. Since Medusans are disembodied balls of energy, he has no voice, and speaks through the other characters. He speaks the above quote through Spock, during a mind-meld.
What are the advantages foreseen for Kollos?
First, currently several of Marpa's nicest features rely on Perl callbacks for their custom logic. Crossing the C/Perl interface is expensive. To a certain extent Marpa lets you bypass this, and to allow this Marpa has evolved its own virtual machine. Kollos will replace this "homegrown" virtual machine with Lua, which will be much more powerful, no bigger, and (I expect) faster.
Second, the current Marpa implementation, which has to support a number of deprecated interfaces and features, is a bit of a morass. This makes it difficult to add new features to Marpa::R2, especially now that it is seeing major usage. But since stability and backwards compatibility are important, I will freeze Marpa::R2, and put new features into Kollos.
Third, Kollos will make the higher layers of Marpa::R2, which are now tightly tied to Perl, available as a C language api. In other words, Kollos will be a language-agnostic high level interface, one that can be made available in other languages.
Kollos itself will be a Lua API for Libmarpa. Lua is a minimal language, but quite useable for many purposes. For example, Kollos's test suite can be written in Lua, so that other languages which port Kollos/Marpa will not need to rewrite the test suite.
Will Kollos be compatible with Marpa::R2?
No. Old features will only be kept based on their merits. Behavior won't be changed whimsically, but it will be changed if there is any good reason to do so.
What will happen to the SLIF?
It will be preserved in Marpa::R2.
Kollos, though, will have a new interface language, the LUIF. It will look like Lua, except that it will also have BNF statements which declare rules. The design of the LUIF is in progress.
Which version of Lua will you use?
Lua 5.1, because it is compatible with the LuaJit. Also because it is the version most heavily supported in Perl.