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

[Sven Luther <luther@dpt-info.u-strasbg.fr>]

On Fri, Oct 18, 2002 at 10:23:32AM +0200, Remi VANICAT wrote:
> 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).

It will just do what you tell it to do, which is a feature, not a bug :)))

Friendly,

Sven Luther
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