Re: Exception types?

[Brian Rogoff <bpr@shell5.ba.best.com>]

On Mon, 15 Jun 1998, Mats Weber wrote:
> Brian Rogoff wrote:
> > It isn't really a workaround, as you haven't really parameterized the
> > package by an exception, and you can't pass that package as a generic
> > formal package parameter. Mats workaround involved passing a success/failure
> > function (an exception "wrapper"), which is a little better in the
> > particular case I'm interested in.
> 
> This is not true, or at least inaccurate (I don't know what you mean by "a
> success/failure function" or an exception "wrapper").

On page 9 of your thesis, you discuss one Ada 83 workaround to the lack of 
exception types, that is passing around a function (End_Of_File) and
assuming that it is checked at places where an exception might be raised. 
That is what I meant by "your workaround", not your actual language
extension proposals.

> My proposal is to add parameters to exceptions, as in Modula-3 (and in Ada 95,
> with the IMO ridiculous limitation to strings of 200 characters).
> 
> In one of the 9X Mapping documents, there was an extension to Ada's exceptions
> that essentially made them part of the type system and you could derive them
> much as you can derive types, thus creating a hierarchy of exceptions.
>

This would be very useful, and would bring one more surly language
construct under the dominance of the package system. 

-- Brian


> > [...] but I was wondering what the thinking was
> > behind not having typed exceptions to begin with in Ada 83. I imagine the
> > reason for not having them in Ada 95 could be upward compatibility.
> 
> The proposal was in the mapping, but was removed. Maybe someone who
> participated actively in the language design can tell us why ?
> 
>