[emfle]

The theory says that for any two programming languages there is a constant c such that any given program can be translated from one to the other with only a c difference in size.

That's just an elaborate way of saying that you can write an interpreter (of size c) for one language in another.

Nevertheless, I have a hard time believing that viaweb could not be written in C short of writing a Lisp interpreter. For that to be true, the runtime compilation of s-expressions would have to be essential to the application; there would have to be no other way to write it.

[pg]

Do you think I would have done something as heavy-handed as compile s-expressions at runtime if it weren't necessary?

We had a page description language called RTML that was Lisp underneath. Users created templates in it, which we then executed to generate their pages. It is these page templates that are still stored on disk as s-expressions in the C++ version.

[emfle]

> Do you think I would have done something as heavy-handed as compile s-expressions at runtime if it weren't necessary?

Why not, if the language makes it simple? I am not claiming that Lisp does not have more powerful abstractions than C, just that they are not usually essential to any given feature in the application.

If Lisp is actually part of the user interface, then clearly there is no way to avoid having a Lisp interpreter. This is begging the question though.