[Aldor-l] exports and constants

[Christian Aistleitner]

Hello,

On Mon, 24 Jul 2006 04:33:34 +0200, Bill Page  
<bill.page1 at synthesis.anikast.ca> wrote:

> In Aldor when we write:
>
>   X: CatX
>
> it means explicitly that the type of X is CatX. And we are
> saying that it is the compiler's job to check (at compile time)
> that this is necessarily always the case.
>
> But 'X has CatA' is something different. I think Christian
> referred to it earlier as something like the "dynamic type"?
> But in the Aldor User's Guide this is just called
> "type satisfaction".

But I suppose, the reason for the whole discussion is that Aldor does  
simply refer to types. Aldor follows the "types on variables approach".  
And "values are not normally self-identifying" (which hopefully means  
something like "values are normally not self-identifying"). So data has no  
type on its own--normally.
Assume Domains are not self-identifying. The whole "has" thing would  
collapse. Because "has" does test on the data, not the type of the  
variable referring to the data.
So domains have to be self-identifying.
Therefore, in a statement

A: B == C;

we have to separate between the type that A is defined to have (which is B  
-- due to the "A: B") and the type of the value of A (which is the type of  
C -- due to A == C).
During my education, I've been given the terms "static type of X" to refer  
to the first concept and "dynamic type of X" to the later concept.

Yes, these two terms are important for type satisfaction. But I do not  
think, "dynamic type" is just called "type satisfaction" in the Aldor user  
guide. Type satisfaction typically acts on the static type of both,  
participing entities. (In the example above A's static type (which is B)  
has to met by C's static type. Not "dynamic type at all.)

"static type" and "dynamic type" may coincide, but do not have to.

--
Kind regards,
Christian