On 11/19/2008 10:22 PM, Bill Page wrote:
> On Wed, Nov 19, 2008 at 3:30 PM, Ralf Hemmecke wrote:
>> 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 do not understand. If two domains are identical than why is there
> any need to "pretend" that they are the same?
You removed too much from my mail (at least if I understand your
question correctly).
equals?(X: LT, x: X)(Y: LT, y: Y): Boolean == {
if List X has ListType Y then {
(x = y pretend X)
} else {
false;
}
}
equals? works on 4 things. X and Y are domains which both belong to
category LT. Now, my construction is a workaround for the missing 'is'
and therefore the compiler (after having interpreted 'List X has
ListType Y') is not (yet) smart enough to figure out that X and Y are
identical and in the 'then' branch y could actually equally be
considered to be of type X (without 'pretend').
If 'is' were part of the (Aldor-)language, then of course, inside the
'then' branch the compiler should not require 'pretend', i.e. 'x=y'
should just work.
But we speak in dreams here. The only thing mentioned about 'is' in the
AUG is that it is a reserved keyword.
Ralf
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