On 2/21/24 21:23, Hill Strong wrote:
Good morning Ralf,
On Thu, Feb 22, 2024 at 4:49 AM Ralf Hemmecke <[email protected]> wrote:
[Remove ...]
Suppose there are two categories CatA and CatB and we define
CatAB: Category == Join(CatA, CatB)
You know that there is a little difference between
FooJ(D): Export == Implementation where
D: Join(CatA, CatB)
Export ==> ...
Implementation ==> ...
and
FooC(D): Export == Implementation where
D: CatAB
Export ==> ...
Implementation ==> ...
You say that there is [little] difference. Why is there any difference? In
one case you have created a name for the Join, in the other it is
anonymous. Yet, the [value] that is the category in both cases should be
identical and hence NO difference between either specification. If there is
then the system has a major problem that is not explained anywhere. The
semantics should be identical.
See https://fricas.github.io/book.pdf page 15: "Domains Belong to
Categories by Assertion",
You may wish for something else, but that's the way it is in FriCAS (and
Aldor).
If we have
Dom: Join(CatA, CatB) == ...
then
FooJ(Dom) is OK, while FooC(Dom) is not.
Again, what difference is there between either case?
Dom is of CatA and of CatB but not of CatAB. FooC requires its argument
to be of CatAB, but Dom is not of that type, so FooC(Dom) cannot be
compiled.
The underlying
category [value] should be the same and defining a domain as you have done
and used in either definition should result in an identical code
production. If it does not then again there is a serious problem with the
semantics and the compiler is going to bite the user and the code
developers in strange and very awkward ways.
You wish something else. That's fine. But the SPAD language implements
"a domain only belongs to a (named) category if that category is
explicitly included when the domain is defined".
There are ideas of "post facto extensions" in Aldor
http://www.aldor.org/docs/HTML/chap10.html or look into the Aldor User
Guide (http://www.aldor.org/docs/aldorug.pdf) that would make life a bit
easier. Unfortunately, SPAD does not (yet) implement this idea.
And it would still be the same. Domains belong to categories by assertion.
Yes, it may make sense to introduce specific categories, like CatAB,
but you then have to go through the whole FriCAS sources and figure out
in which cases you might have to add something like CatAB to the exports
of a certain domain (or category, and maybe even conditionally, i.e.
depending on a domain parameter). That is doable, but sounds a bit
error-prone. I don't even know whether it is easy to check that such a
code modification did not introduce unwanted behaviour, because we might
There should be very very few cases (zero or close to it) where such
changes would be different semantically. If there does arise differences
then the underlying compiler (boot) is the problem and needs seriously to
be fixed.
You can see it that way. However, the current behaviour *is* documented
and the compiler behaves accordingly.
FriCAS has a high enough learning curve as it is, without strange little
semantic anomalies coming out and biting you like some yapping little
ankle-biting dog at unexpected times. I fully understand that any code
base, especially one as old as this, will build up a lot of cruft over its
lifetime. But it does need to be dealt with or the code base will become
unmaintainable in many ways. Making little ad hoc changes here and there
does not garner well for the system's future where you want more people to
be interested in and actively use the system. Axiom and FriCAS both deserve
better as does all the hard work that has been put into each by all the
people who have been involved over the decades.
If you can help to make FriCAS better, you are welcome.
As for the learing curve... I usually point someone who wants to learn
SPAD to reading the Aldor user guide (AUG). Yes, Aldor is a bit
different from SPAD (I once listed a number of them here
http://wiki.fricas.org/LanguageDifferences), but the AUG much better
defines the language than the FriCAS-book does.
Ralf
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