For a programmer without Lisp experience, that would be true. But I've written enough Lisp-based webapps that there aren't really that many 'unforseen' problems for me anymore (rule of thumb: use software by Edi Weitz - everything he writes is golden :-D)).
That being said, I still ran into trouble with Elephant, so I probably should have taken these sort of 'unknown unknowns' (which are more prevalent in unusual languages like Lisp) into consideration upfront. To not do so was certainly an oversight.
If you are going to be the only programmer on the project then your reasons make sense. However, if you are going to have other people on the projects - then your reasons do not make sense from a longer term point of view. How many lisp programmers do you have out there as compared to python or ruby programmers? If you and the founders decide to go your separate ways how likely is the project going to be continued in lisp?
It seems like a somewhat precarious decision to let you use Lisp for this project. There's nothing supremely special about the problem you are attacking that warrants Lisp (outside of your comfort level which you clarified very clearly in your post).
Perhaps I'm just old and cynical but I've been on too many projects where the first (and therefore "lead") developer chose a particular language and architecture that in the long term was not sustainable.
There are, obviously, far more ruby/python programmers. But, at the very most, I might only ever need a dozen Lisp programmers and I already know 20 that I would love to work with. Lisp is even pretty easy to pick up if you're smart know other dynamically typed, functional, and OO languages.
As a point of reference, ITA Software has no trouble hiring 100s of Lisp programmers.
Minor correction: I am a founder - and if I were to leave (while my co-founders continued), I'd make a point to find my replacement first.
"How many lisp programmers do you have out there as compared to python or ruby programmers?"
This one is a tired argument. Any good programmer will grok Lisp (or Python, or Ruby). If your Python/Ruby programmers can't get Lisp from a couple days of training, then they are not good programmers.
And, BTW, I would risk betting they are writing FORTRAN code in Python and Ruby.
For a programmer without Lisp experience, that would be true. But I've written enough Lisp-based webapps that there aren't really that many 'unforseen' problems for me anymore (rule of thumb: use software by Edi Weitz - everything he writes is golden :-D)).
That being said, I still ran into trouble with Elephant, so I probably should have taken these sort of 'unknown unknowns' (which are more prevalent in unusual languages like Lisp) into consideration upfront. To not do so was certainly an oversight.