[taneq]

Absolutely true, and it sounds like you're doing really interesting stuff where the language and the way it maps to the problem are more important than the factors I listed above.

Do you stick with the same (maybe-)esoteric language for the production implementation? And if so, does this then drag the rest of the production implementation into that language as well, or do you do the hard bit in one language and the routine stuff in another more common language?

[sterlind]

I do the hard bit in the esoteric language, then the glue in a traditional language. for instance, I made a tool that exhaustively steps an implementation through every possible state of a TLA+ model. I wrote "serializers" to parse TLA+ expressions into C# classes and vice-versa, and used this to build a bridge. Parser combinators work great for this stuff, though that's another reason I'd be happier with a Lisp representation for everything.