someone wrote:
>
> Hi,
>
>
> > The following works, but is (of course) not the right solution.
> >
> > rows(A:M, si:SPI) : M ==
> > rows(A, (expand(si pretend Segment(Integer))$Segment(Integer))
> > pretend List(PI))
>
> Yes, this would work.
>
> > > (1) -> PI has ORDRING
> > >
> > > (1) false
> >
> > > This means I can not expand a Segment(PI) into a List?
> >
> > Exactly.
>
> Too bad. OTOH the interpreter can do it without any hassle.
>
> > > Why not, it seems to be a natural operation, no?
> >
> > Right, but the current library implementation is unnecessarily
> > restrictive.
> >
> > I guess for "expand" we only need OrderedSet, a distinct element 1
> > (default step size) and an operation +. In fact, disregarding the "by"
> > construction of a segment, a function next: %->% would be enough.
>
> Maybe we should try to lessen these restrictions?
> What do you think about this, would it be feasible
> or rather introduce new trouble somewhere?
Note that internally a Segment always has an _integer_ increment.
So, to be sure that expand succeds you need to make sure that
there is a coercion from Integer to the base type. I am not
sure if in practice this gives more generality than just
requesting OrderedRing -- at least there is no coercion from
Integer to PositiveInteger.
I am affraid that to fix this one has to reorganize Segment
quite a bit:
- require that argument is a join of OrderedAbelianSemigroup
and Monoid (to have 1)
- change increment to be of the same type as base
- update algebra, interpreter and Spad compiler to cope with
non-integer increments.
> (87) -> )display op coerce
>
> There are 86 exposed functions called coerce :
> [1] D1 -> D from D if D has ALGEBRA(D1) and D1 has COMRING
>
> >> System error:
> The value D2 is not of type SEQUENCE.
>
> What happens here? I think this is a bug, isn't it?
Yes, a bug. Need to track what exactly causes the problem.
--
Waldek Hebisch
[email protected]
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