> Are programs written to make heavy use of exceptions going to be markedly
> slower than programs written more traditionally with loops/ifs, etc?
> (My uninformed mental picture of exception is that they would use
> some type of underlying setjump/longjump overhead.)

The OCaml compiler "knows" about exceptions, so it can implement them
more efficiently than setjmp/longjmp.  Namely, there is no need to
save registers to install an exception handler and to restore them
when raising an exception.

As rought approximations, I would say that raising an exception costs
no more than, say, two calls to unknown functions, and installing an
exception handler costs no more than one such call.

- Xavier Leroy