That said, I do wonder at times what it is about Lua that makes so many people not-interested in it, when .. from my naive point of view .. its an almost perfect language for rapid development. I don't have that feeling about Python, quite so much ..
Lua doesn't have a lot of features. This is great because it's small and simple to learn, but it makes some jobs harder. As I'm not a great programmer, there are features that people could write themselves, but that's beyond my skill level. I'm constantly pushing tasks to the OS level, which makes my code one step above a Bash script. Other times I'll push something to C, which turns friendly code into a death trap.
Lua needs some love and care from the community and it would be perfect. Python has that love and care, but it's still a mess (IMO) at the core language.
Probably because the core language is only a small part of what determines a language's usefulness. Python has heaps of tools and libraries, is used in many software packages as the scripting language, and is generally well-known by scientists. Who cares about syntax, really. It's the ecosystem that makes a language powerful.
They don't adopt it because the ecosystem is so much smaller, as I said. Chicken and egg, and Python had the first mover advantage. I embedded Python from C++ in less than a day too, that is not the problem. It's the design of the API for the integration which takes the work.
I'm a user of both, fan of both, but the lightness of Lua is a big plus.
The main downside, IMO, is that the Lua user base is smaller so there's more need to roll your own solutions for things that Python already has several libraries for.
Lua the language and LuaJIT the third party vm are great. But there is no general purpose standard library. Like in C one has very limited libraries that are shipped with Lua - that's fine. Though I really miss a good website with a list of additional up-to-date libraries and a community around it.
Lua needs a better project website, like PHP where you can post code examples as comments. At the momemt the Lua website is stuck in 1999. The wiki software is bad, the only way to stay in touch is the mailing list, etc. The LuaForge website is outdated. Finding various libraries is pain. Many libraries are hosted on servers that don't exist anymore or are for Lua 4 or 5.1 but not 5.2.
A lot of users use Lua in closed source software as embedded language (video games, Adobe programs, etc.)
Imagine if all those libraries that you find for Python would be available for Lua, it would be great.
Because:
From 1977 until 1992, Brazil had a policy of strong trade barriers (called a market reserve) for computer hardware and software. In that atmosphere, Tecgraf's clients could not afford, either politically or financially, to buy customized software from abroad. Those reasons led Tecgraf to implement the basic tools it needed from scratch.
But the everything-is-a-string [1] semantics is awkward to deal with. As with shell scripting, a lot of what you do amounts to solving problems with quoting. I find Tcl hard to debug, and I don't like the scoping (upvar!).
I'd much rather use Emacs Lisp. In fact, Cadence uses a language of their own, called Skill, for some of their tools. It's so close to Emacs Lisp it may as well be identical, and it's far easier to deal with than Tcl.
[1] That's no longer true under the hood. But Tcl behaves as if it's true.
The great thing about Lua is that tables - or, rather, metatable programming - is really, really powerful. I'm finding it difficult to think of an example of a common, powerful data structure that we all know and love, which can't be implemented with Lua tables/metatables. Lists, hashes, arrays, tries, trees, all of these basic things work so well in the context of the Lua table.
However, you have to learn what a table is, in Lua. You have to learn how to use it effectively. A lot of times, folks don't take the effort to understand how metatables can be used to turn your average Lua table into .. objected-oriented constructs (classes), queues, stacks, etc. But if you do make at least this milestone in learning Lua: watch out! You won't want to use any other language, ever again! :)
Scientific libraries for Lua: http://stackoverflow.com/questions/388172/scientific-librari...
"A Primer of Scientific Computing in Lua" (book chapter in "Lua Gems" book), source code: http://code.google.com/p/luagems-numeric/downloads/list
LuaTex, an extended version of pdfTeX using Lua as an embedded scripting language: http://www.luatex.org/