Again, I think the limiting factor is not ease (nor compilation time), but trust in robustness. There's no point in making an "extensions design for Dummies" system, because nobody wants to use an extension written by a dummy. It won't be easy to write an extension; what should be easy is:
On Jan 23, 2008 12:10 PM, Asko Kauppi <email@example.com
However, doing all the necessary precautions can be made in many
Everything computable can be done with any Turing-complete language. But to make it practical, you need the proper abstraction level; if a system requires to reimplement half of metalua to get a comparable expressiveness, it's abusive to claim that it "can be made".
In particular, luaSub seems to me syntax and scope
aware enough, that it shouldn't be much harder there. Just to make
sure, luaSub's mods are made in 100% Lua, not in a "low level language".
I mean low level in the Alan Perlis sense: "A programming language is low level when its programs require attention to the irrelevant
With the wrong libraries and APIs, all languages can be low level. In the mod samples provided with luasub, you're still fighting with literal syntax matters when you're trying to perform semantic operations. That's the wrong level of abstraction: you've got more than enough to chew with semantics, so you need to be completely freed from concrete syntax concerns.
A luasub mod essentially plugs callbacks into the token stream, and its
"access" to the AST is limited to having some named entry points where interesting bits
of the tree are about to be parsed; it doesn't really
give a direct grasp on the only right mental model (trees), and you can't describe non-trivial search and
transform on them (at least not in a robust, readable and maintainable
way). When splicing trees together, mods are directly piping token
streams together, that's only marginally higher level than string
processing; try to do some capture analysis on the fly and your code will become absolutely ugly (and proably wrong as well).
For instance, you want to think of an upvalue as <<a reference to a bound identifier that's separated from its binding statement by at least one function declaration>>, and that's mostly the way you'd describe it with metalua's
. You're doomed if you try to think of it in terms of:
<< a list of ids that's after a "local" or "for" or "function"+"(" or "local"+"function" keyword, then followed by more "function" keywords than "end" keywords related to a "function" one, and with no "local"/'for" keyword introducing an homonym function in between >>.
It is theoretically possible to use such abstractions (although I'm myself really not confident in the stream-oriented description above), the way it's theoretically possible to write a complex web application in pure C. Your code will become unexploitable very soon. too soon to write anything useful and robust IMO. For that level of power/abstraction, I think m4+Lua or Luma offer similar capabilities under a much better better interface.
I think most people will flock around once the solutions are so simple they hardly see them anywhere.