Re: Queue

["Ehud Lamm" <mslamm@mscc.huji.ac.il>]

Brian Rogoff <bpr@bpr.best.vwh.net> wrote in message
news:Pine.BSF.4.40.0111300447310.89131-100000@bpr.best.vwh.net...
>
> The excessive instantiations that you need in an Ada version of the STL
> become ponderous IMO. I believe this is a fundamental problem with Ada
> generics, and perhaps even a fundamental issue in statically typed
> languages, namely, when do we prefer explicit (manifest?) types and when
> do we prefer implicit types. My own opinion is that I'd like a language
> with both. Ada has only the first, and while modern high level languages
> (think ML and Haskell here) provide both I'm a bit unsatisfied with the
> way it all fits together (not to drift too far, but I'd like something
> like Haskell's type classes and not just ML's universal style of
> polymorphism, *and* I want a decent module system). I guess I'm not meant
> to be happy with any programming language :-).
>

I am with you on this.
In a sense this is a language engineering issue. We want to safety brought
by explicit instanations etc., but we don't want to have to use it all the
time.
I am still not sure what's the best way of combining these features, but it
seems to me there shouldn't be a theoretical problem here, just a need for
smart language design.

> Just so I don't sound entirely negative, generic formal package
> parameters, and the signature trick, really make something like the STL,
> or Bishop's approach, a lot cleaner in Ada 95 than was possible in Ada 83.
> It also makes the STL easier to understand, since you can express the
> notion of "iterator category" (I think that's what Alex Stepanov called
> it, I can't remember since it was a few years ago) pretty directly with
> a few signatures (Forward_Iterator_Sig, Bidirectional_Iterator_Sig, etc.).
>

Signature packages are a very important concept, and add expressive power
that I like.
Indeed, formal packages were a great addition to the language. But they can
be improved upon (for example, I'd like to be able to elegantly require that
 two formal packages share some parameters, etc.)

Ehud