Re: [Caml-list] Re: Camlp4 optimizations (was: productivity improvement)

[Remi VANICAT <vanicat@labri.u-bordeaux.fr>]

Alessandro Baretta <alex@baretta.com> writes:

> Jeffrey Palmer wrote:
>> On Thursday 17 October 2002 6:55 pm, Alessandro Baretta wrote:
>> Hmm. I have two observations:
>> 1) You can't "use" templates without instantiating them, so although
>> you're right - template type checking is deferred to instantiation,
>> this is by design (a pain, I agree).
>
> It's more than a pain. John Max Skaller acutely pointed out that
> templates have "no semantics". The semantics of a template depends on
> the parameter(s) with which it is instantiated, and in a very bizzarre
> way. Code which compiles and is correct with well-behaved
> parameters--the STL, for example--becomes incorrect, won't compile, or
> will miserably die at runtime with a segfault, if it is instantiated
> with a parameter class redefining the basic operations--equality,
> assignment, copy constructor, etc--in a such a way as to violate the
> assumptions explicitly or implicitly made by the template
> designer. Such errors are not revealed when the template is written
> and "compiled". They are revealed at best at template instantiation
> time, and possibly at runtime.
>
> Caml functors, on the other hand, are statically type checked at
> compile time. Once and for all. If they compile, they're correct. And
> that's it.


Well, the Set.Make and Map.Make functor to the stdlib want the compare
function of their argument to be a comparison function. This in not
checked at compile time (this can't be verify). and if this not the
case, you can difficultly predict the comportment of those functor.
(well it won't segfault, but it may not do what you want).

SO it is not so simple.

>> Oh, and in response to my own earlier question regarding partial
>> evaluation and strongly-typed languages, I noticed a post elsewhere
>> on the list to a very interesting site:
>> http://www.cs.rice.edu/~taha/MetaOCaml/

There is also dml (http://oops.tercom.ru/dml/) that don't need a
patched version of ocaml...
-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat
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