Dear Waldek,
On 7/19/25 14:32, Waldek Hebisch wrote:
%%% (227) -> R ==> MultivariatePolynomial(['a,'b], QQ)
Type: Void
%%% (228) -> C ==> Fraction R
Type: Void
%%% (229) -> U ==> Polynomial C
%%% (232) -> "x"::Symbol :: U
Polynomial(Fraction(MultivariatePolynomial([a,b],Fraction(Integer)))
) is not a valid type.
> Look at 'isLegitimateMode' in clammed.boot: it rejects types where
> inner and outer polynomial variables intersect.
For me
monomial(1$U, "x"::Symbol, 1)$U
which avoids ambiguity works.
Hmmmm... that now makes me wonder when the 'isLegitimateMode' actually
is applied/called. I seem to remember that I could achieve a working
situation (though I used Polynomial and below some multivariate
polynomial type) in compiled code.
Your 'monomial' construction and also a working 1$U seems to suggest
that not the type itself is problematic, but the (auto-)coercion.
Understandble.
Anyway, I have looked at 'isLegitimateMode' and must say, that I am
somewhat unhappy with it. The reason is that it lists explicitly some
types like Polynomial, Expression, Complex. I understand that this might
have been done to prevent users from running into troubles later,
however, coding that logic in BOOT and not SPAD, but with explicit
identifiers from the SPAD library, I don't know... If I now go and
invent a new polynomial domain. It is certainly not covered by this boot
logic. Yes, yes, I don't know how to do it better, still I feel uneasy
about it.
Anyway, if I use a construction like your 'monomial', i.e. create an
element of a domain like U that has no ambiguity in its creation, can it
happen that I will ever by bitten later (always assuming that I never
use any of the function that potenially are ambiguous. i.e. depend on
variable names/symbols)?
Technically a type like Polynomial(Polynomial(INT)) is not a problem and
%%% (9) -> PPI ==> Polynomial(Polynomial INT)
%%% (10) -> one := 1$PPI
(10) 1
Type: Polynomial(Polynomial(Integer))
seems to confirm this. But then why doesn't the following work
%%% (12) -> ppi:PPI := 1$PPI
Polynomial(Polynomial(Integer)) is not a valid type.
Obviously, (12) triggers a call to 'isLegitimateMode' whereas
(10) does not.
Suppose, I create a type
Foo(C: Ring): Polynomial C == ...
If I am careful with constructing the element of the return type (like
your 'monomial' above), would such code compile even if I later
instatiate Foo(Polynomial(INT))?
I (as a user) are aware of the potential variable overlap, but take care
of that myself. My question is whether SPAD might prevent me at some
point from doing this or kick in (via BOOT code) at some unexpected places.
Maybe this question is too hard to answer, but maybe you happen to know
and have some experience. For now I could live with a restriction of
being unable to call Foo(Polynomial(INT)), but it would be good to know
whether I must think of something else if ever I have need to call
Foo(Polynomial(INT)).
Thanks in advance.
Ralf
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