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Lightweight Scripting/Extension Languages?
Andy Tai asks: "Extension languages are designed to be embedded in applications to support customization of the application behavior. Common scripting languages, like Perl and Python, are fairly 'large' with powerful run-time engines and libraries and are widely available and 'script' writers usually assume their stand-alone existences in the deployment environment. However, if one is looking for a language that's small enough so its source can be embedded in the distribution of and built as part of the application, Python and Perl may be 'overweight.' For the real lightweight choices there are Lua and Tinyscheme. Are there others? What are people's preferences and opinions regarding lightweight extension languages?"
Is usually a sign that you are using too low-level a language for the application itself. There is no reason you can't write your whole app in something like Python (or better yet, a compiled high-level language).
I can see why you might want to stay with C/C++ for a major commercial application (not because of speed reasons, but because the maturity of the implementations of alternative high-level languages) but it pains me to see tons of OSS software, especially non-speed-critical GUI apps, still being written in C!
A deep unwavering belief is a sure sign you're missing something...
Tcl/Tk proper is not a bad idea either. If one does not need the GUI part (Tk) then Tcl is relatively easy to integrate into a project, and is under 200k.
HowToEmbed from the Tcl Wiki is a good starting point, and MkTclApp may help.
Tcl has very consistent and simple syntax (although it can get rather confusing at times), and it is very simple to add new command into your application that are exposed via Tcl. One of the nicest aspects of Tcl is that is it seriously multi-platform.
Of course this all depends on the requirements: how powerful does the language need to be, what functions must it provide, what types do you need it to be able to handle, how small is "lightweight", etc.
i-name =twylite [http://public.xdi.org/=twylite], see idcommons.net
ECMAScript/Javascript seems like a logical choice. it was made for just that - embedding. It's quite small to implement, and there are many opensource implementations out there already. It can be procedural or OO, and everyone knows how to use it if they've done some basic web work.
TinyPerl
Error: PANTS NOT FOUND. Press <F1> to continue.
ficl.sourceforge.net
A portable object oriented forth at less than 100K for a full implementation, able to handle calls from your apps as well as call your apps fgunctions or other dll's.
Under a BSD-ish license.
The upside:
1) Its tiny
2) The forth code you write will be tinier
Downsides:
1) You need to learn forth (I mean properly) to appreciate it.
Forth is unlike most other languages, it was designed to avoid the debug, recompile cycle that is so common.
Sam
blog.sam.liddicott.com
Another nice aspect of Tcl is that it can easily evaluate code in a different stack frame (example: in the caller's context), and source code can be easily passed to procedures as strings between braces (as it is usually done), so extending/reimplementing the language control structures is as simple as writing a new procedure (and no special/ugly syntax is required).
That's as close to Lisp macros as you can get.
I've been working on a system for embedding JS in KDE apps (amongst other reasons it is a about 1/10 the size of a python interpreter). You can find lots of information at http://xmelegance.org/kjsembed. The interpreter in KDE has no dependency on KDE/Qt or anything else so you might find it usable in your app.
Well you're not obligated to provide the libraries. For instance, Blender, which uses Python, did not include Python libraries ; however it was possible for people which really wished it, to set paths to point to libraries. Forcing the users to learn a new language, just to cut the size of the distribution is misguided IMHO. Just provide the extension language (& support) as an optionnal individually downloadable shared library.
Ferite is a scripting language and engine all in one managable chunk. It is designed to be easily extended in terms of API, and to be used within other applications making them more configurable and useful to the end user. It has a syntax similiar to a number of other langauges but remains clean and it's own language.
I love that it was designed from the Start to be Thread Safe and Embeded, unlike PHP or Python.