I dunno - most LFSP-people I know use multiple languages regularly, learn new ones as a hobby, and their "preferred" LFSP is just the top of a long list of skills. That's why we call them "smart people". ;-) Take a look at Programming Reddit - most of the Haskell evangelists are also quite fluent in Python and C and usually know Lisp, Ocaml, etc. too.

There do seem to be exceptions - Common Lisp in particular seems to be a LFSP where many of its leading practitioners only know Lisp. Smalltalk, too, but to a lesser extent since all the commercial Smalltalk jobs morphed into Objective C or Java jobs. But I don't really see Lisp as being at the top of the blub hierarchy any more - there's been 20 years of progress since then and some really interesting developments.

"Common Lisp in particular seems to be a LFSP where many of its leading practitioners only know Lisp."

The hardcorest Lisp hacker I know wrote the chapter on C++ in the UNIX Haters Handbook. He also wrote a C to Lisp compiler for the Symbolics Lisp Machines. (And he works as a C++ programmer right now. :-))

UNIX Haters Handbook, published in the early 90s: http://research.microsoft.com/~daniel/uhh-download.html

I'm not so sure. Most of the Common Lisp people I've met know Java. I can't think of a single one who doesn't know C.

Or did you mean Common Lisp people tend to have only that language as their LFSP, no matter how many LFMs they know? In that case I would agree - I definitely see CLers ignoring Ocaml, smalltalk, etc. For my part I guess it's because CL took a long time to learn fully and I need to build up some energy before I invest that amount of time in another LFSP.

I'm a game developer. At work, we use C++, C# and our own scripting language. Our language is embedded, so the communication protocols between C++ <-> our language are straightforward, and C++ <-> C# happens through function callbacks.

At home, I use C++ plus Lua. I tried to use Lisp, but the CFFI had problems interfacing with certain foreign libraries.

To get around C++'s constraints, my solution is to move all of my game engine code to Lua with only a lightweight wrapper in C++. Lua is extremely powerful - for example, functions are first class objects, so it has closures. It's dynamically typed, so I'll spend less time convincing a compiler I should be able to run my code. It's very fast, because it has a JIT compiler which uses DynASM to generate assembly code, so it's about 1/10th the speed of C - huge for a scripting language. But most importantly, the communication protocols between Lua and C are extremely clearly defined, and work. Communication between Lisp and C is much more vague, and only sometimes works - Calling Lisp from C, for example, don't work on all platforms.

So I'd guess what influences me in my choice of multiple languages is how well two languages can communicate with one another. Can all constructs from Blub translate into Floob? How does Blub call into Floob, and vice-versa? Is it supported on all platforms? Is there a lot of example code?

You can certainly have a language mashup and solve problems in elegant ways, but it all hinges on how elegant the communication is.

If you use several different languages, and if they don't share resources (Window handles and such), and if communication between them is not speed-critical, then you can write a networking layer which each language uses to communicate with every other language. But that option seems pretty rare.

Shawn