Regarding Reilly Hayes’s last comment, using ad-hoc polymorphism to overload the “+” operator, as SML does, is clearly a trade-off, with SML requiring a slight extension to the type system, giving slightly more obfuscated error messages and even introducing discrepancies between the types inferred by different compilers.

You could implement a numeric tower for OCaml using camlp4 but this would give worse performance, complicate interfacing (including with the stdlib) and would only work on a per-source-file basis.

I do miss the freewheeling nature of runtime type checking with Lisp, especially for prototyping (but my code also seems to have fewer bugs with OCaml, so I suppose it’s a tradeoff). I’ll probably get a Scheme up & running in OCaml at some point to get some of those advantages back, but the problem then will be getting enough primitives up and running to make it worthwhile to prototype anything (that is one thing I miss about .NET—while reflection is slow, it does eliminate the need for a Foreign Function Interface).

I’ve only done really basic things with the OCaml object system so far, but other than the need to manually downcast objects and the poor error reporting for syntax problems for class definitions, I’ve been fairly happy with it.

I’ve never used multimethods, but Mike Vanier had a similar falling out with OCaml over the object system & lack of multimethods support .

The Oreilly OCaml book has an interesting comment about the object system as well:

“There is no class hierarchy in the language distribution. In fact the collection of libraries are supplied in the form of simple or parameterized modules. This demonstrates that the object extension of the language is still stabilizing, and makes little case for its extensive use.”

I haven’t tackled camlp4 yet. I go back and forth on macros. On one hand they are indisputably powerful. On the other hand, having a malleable syntax can be quite confusing. In any case, macros are great for implementing Domain Specific Languages—Shriram Krishnamurthi’s automata example in his The Swine Before Perl presentation is pretty compelling.