I’m currently working on a scriptable simulator for a firmware. At first, I was going to script it using Pything: a nice, object-oriented language that can be embedded into C++ using Boost.Python. I soon (well, soon… after a morning of trying) found out that it was not going to be as easy as I though, though, because the version of Boost I have to work (1.33.1) with wasn’t going to be of much help so, after coming to the conclusion that if I was going to do this in the time I’d planned for it, I’d have to change my strategy.
In terms of scripting languages that are easily embeddable into C++, there aren’t too many to choose from. Python can be a good choice – but turned out not to be in this case – but if that doesn’t work and you still need to use a language that embeds easily and doesn’t cause too much of a head-ache in the embedding, I for one turn to Funky pretty quickly. that might be, of course, because I am its author but it also happens to have almost all the features I wanted in there – except for looping.
Since version 1.3.00, there is some support for looping in Funky, using the auto-recurse feature. A very trivial example, taken right from the Funky test case source code, looks like this:
((add, @@), 2, @@)
which is equivalent to
(add, (add, @@), @1)
The current version of Funky does not support looping on predicates, however, so the following would not work:
((add, @@), (pred), @@)
which would be the equivalent of a while loop.
Jon Dahl wrote about functional programming and looping here and is quite right in saying that a functional approach to looping is very often superior to a procedural approach. However, even Lisp supports a while loop, as does Scheme, so I don’t think I’m too far off with what I came up with.
What I did come up with is sufficiently different from the auto-recurse feature to not be confused with it, and actually looks a lot like the lisp and Scheme variants:
(while, (condition), (body))
in which the body is optional, meaning you can loop forever on a predicate. The condition may also be a parameter or a literal, meaning you could, if you really wanted to, loop forever.
But why does Funky need a while loop?
The answer is simple: Funky is an embeddable functional programming language, meaning that the function it calls as a predicate may very well be a function written in C++. If that is the case, it could do anything. In my case, it will be reading from a socket.
I think I’ll add this feature to the next major version of Funky, which will be 1.4.00.