> 'is' however is something else. It invites the programmer to deal with
> specific cases rather than the most general case.
I'd would discourage 'is' for such a case.
In some experimental code, I had myself some need of 'is' in Aldor.
Since there is no 'is' I used some workaround.
Here I don't need it for selecting special cases, but rather to check
whether the domains are identical so that I could safely 'pretend' that
one value 'y' of type Y is also of type X.
Instead of the line
if List X has ListType Y then {
you should read
if X is Y then {
.
I don't say that I am completely happy with the code at all, since
'Object' as presented in the AUG is not really one of my favourite
types. (Same for Any, but this is a another story.)
Ralf
---
define ObjectLabelType: Category == with {
LabelType;
label: (Lab: LabelType, Lab) -> %;
explode: % -> (Lab: LabelType, Lab);
}
Label: ObjectLabelType == add {
macro LT == LabelType;
Rep == Record(LabDom: LabelType, label: LabDom);
import from Rep;
label(Lab: LabelType, l: Lab): % == per [Lab, l];
explode(x: %): (Lab: LabelType, Lab) == explode rep x;
equals?(X: LT, x: X)(Y: LT, y: Y): Boolean == {
-- We must check whether X is the same domain
-- as Y. We can do that by asking whether
if List X has ListType Y then {
(x = y pretend X)
} else {
false;
}
}
(x: %) = (y: %): Boolean == equals?(explode x)(explode y);
...
}
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