Re: stopping a loop iteration without exiting it

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 18-01-06 19:20 , Dmitry A. Kazakov wrote:
> On 2018-01-06 17:50, Niklas Holsti wrote:
>> On 18-01-05 10:38 , Dmitry A. Kazakov wrote:
>>> On 2018-01-05 00:08, Niklas Holsti wrote:
>>>> On 18-01-04 23:17 , Dmitry A. Kazakov wrote:
>>>>
>> If we have
>>
>>     type Root is tagged ...
>>
>>     type T is new Root ...
>>
>>     type U is new Root ...
>>
>> the T'Class and U'Class do not overlap. But if "U is new T ..." then
>> they overlap.
>
> And what will be selected? The semantic of case is of mutually exclusive
> choices, so that the order of the choices were irrelevant.

Well, that was what I suggested, that the "case" would require all 
choices to be non-overlapping, and therefore mutually exclusive.

Yes, in generics it would not always be possible to decide whether two 
formal types overlap, so either the "case" would be illegal there, or it 
could be defined as a non-deterministic choice.

> ... But that would require type ranges (see below) to resolve clashes

    [snip]

> T is a single type. T'Class is a range of types similar to
> 5..Integer'Last. Certainly definite ranges of types must be supported as
> well:
>
>    X in T..S
>
> which same as
>
>    X in T'Class and T in S'Class and (X in S or else X not in S'Class)

That is a bit hard to understand. Are you mixing into this condition 
both a definition of when T..S would be a legal "type range", and a 
definition of the membership test, X in T..S? Please clarify.

> But the point is that it is the type of X not its value as it appears
> when reading "case X is".

For class-wide types, the "type of X" (i.e. the tag of X) is part of the 
value of X, IMO. But I would not mind if the syntax would require "case 
X'Tag is".

However, I do think there is a clear (and perhaps valuable) difference 
between the forms

    when Same_X : T =>

where the object Same_X would not be class-wide, and

    when Same_X : U'Class =>

where the object Same_X would be class-wide. One could admit both kinds 
of "when" in the same "case", of course, as long and they are 
non-overlapping.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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