On Sun, Feb 21, 2021 at 05:53:24PM +0000, Peter Broadbery wrote:
> >
> > > IIUC Aldor does not suport "failed" (with Spad notation) as a type,
> > > which leads to massive source changes (this is in the language
> > > differences page).
> >
>
> Aldor does allow 'Union(a: T, failed?: 'failed'), which might be similar
> enough.
> Tangentially, what would be the issues with switching the algebra code to use
> Partial instead of the Union?
Well, I do not know what Partial offers. In particular, what we
gain from using Partial instead of Union. Concerning "failed"
and similar, it is not only Union(T, "failed"). One can have
multiple alternatives or multiple failure modes.
If we replace Union(T, "failed") by something else we would
handle most cases of such types. Some other could be converted
to Enumeration. OTOH, talking abtractly Spad has notion
of singleton types: types with only one value. Such types
seem to be useful and Spad notation (as a string) looks reasonable.
It is not clear for me what we gain by eradicating such
types (or at least current notation for such types) from
the language.
--
Waldek Hebisch
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