Re: [boost] Boost::Tcl (was: Boost::Ruby)

From: Maciej Sobczak (prog_at_[hidden])
Date: 2005-10-01 11:47:49

Pavel Vozenilek wrote:

> You may perhaps take some inspiration in these Boost-like language bindings 
> I know about:
> 
> - http://cpptcl.sourceforge.net/ C++ interface for TCL
[...]

> These would likely deserve place in Boost but AFAIK they weren't suggested 
> for review yet.

Which is inaccurate.

C++/Tcl was announced at Boost almost one year ago. After that I was 
suggested to bring it to langbinding, which is an effort to provide a 
universal back end to any language. At that time, the following two 
things were (and still are) clear to me:

1. Different scripting languages and the abilities of their interpreters 
can be sooo different that finding a universal ground for all of them 
would take years of design only. In fact, I don't believe that any such 
universal base will be ever created, if not by finding a common 
denominator which unfortunately might not be satisfying to anybody.

Example 1: Tcl has a type "system" that is fundamentally different from 
that of Python. In particular, in Tcl the type of a variable does not 
depend on how the variable is set, but rather on how it is queried. For 
example, the value "Boost" can be seen as a 5-char string, but "0" can 
be used as *every* type in Tcl, be it bool, integer, string or even list 
(whose only element can be again treated as any type, depending on how 
we want to look at it) - this is very different from how the types are 
treated in Python and largely influences what can be done on the binding 
level. On the other hand, Tcl has no built-in (ie. on the interpreter 
level) support for classes and inheritance, whereas Python has it.

Example 2: Tcl has an object-based approach to interpreters and there 
can be *many* of them, even completely independent (this includes the 
possibility to run them in separate threads). Any given interpreter can 
be made "safe" by disabling certain commands, so that it is very easy to 
create "jails" or "sandboxes" - very useful for applications that need 
to execute untrusted scripts. In addition, it is possible to alias 
commands from one such interpreter to another, which makes it even more 
interesting.

In other words, a "universal" binding would need to be full of 
fundamental compromises.

2. I don't see any *benefit* from building such a "universal" thing. I 
think that users of different scripting languages form rather disjoint 
audiences and any overlap here is too small to justify the effort to 
create a universal language binding.

These two were the reasons for C++/Tcl to go ahead alone. In retrospect, 
I think it was a good decision, especially if we take into account that 
C++/Tcl is now a mature project with growing and interesting user base 
and that at the same time langbinding did not do any progress.

Having said that, I take the opportunity to remind C++/Tcl here (well, 
*you* did it first :) ). It was inspired by Boost, uses Boost and has 
the old Boost licensing scheme. If during the last year the objectives 
of Boost wrt scripting languages changed from what it was a year ago, 
then I will be pleased to see it considered as a candidate for Boost.

Here's the link again:

http://cpptcl.sourceforge.net/

-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/