How to declare my package's parameter properly?

[Neven Sajko]

In the process of writing some Spad packages, I realized that I need
to generalize one of them by introducing another package parameter,
because one of the types would need to be determined by the caller.

Source file: https://gitlab.com/nsajko/fricas_guessing/-/blob/master/guessing_helpers.spad

The package is GuessingHelpers, and the problematic parameter is "In".
Before I tried to turn it into a parameter, it was simply defined as
Fraction Integer, however I want to generalize the package so that In
can be either a Fraction Integer or a Fraction Polynomial Integer.

For a start, I declared In like this:

In: Join(Field, CoercibleFrom Integer, CoercibleFrom Fraction Integer)

However, this predictably fails, as my package requires In to be
coercible to Expression Integer.

If I declare In like this:

In: Join(Field, CoercibleFrom Integer, CoercibleFrom Fraction Integer,
CoercibleTo Expression Integer)

Then I can't construct the package because Fraction Integer doesn't
have the CoercibleTo Expression Integer category.

How should I declare In?

Is it possible to declare a package parameter so as to enumerate a set
of types, and saying that the parameter has to be a member of that
set? This would work for me, I could simply declare In as "either
Fraction Integer or Fraction Polynomial Integer".

Thanks,
Neven

[Ralf Hemmecke]

Obviously that what you want does not exist.
Unfortunately, I am not a user of the Guessing package to be able to
give you a suggestion just so.

To get a rough idea of what you actually want to achieve by
GuessingHelpers it would be very helpful to know what (for example)
the function guess_func_level_1

https://gitlab.com/nsajko/fricas_guessing/-/blob/master/guessing_helpers.spad#L187

is supposed to do. Can you also give example calls (i.e. actual
parameters) for that function.

Maybe then I would be able to give a suggestion for such a helper package.

If you just want the *two* Fraction Integer and Fraction Polynomial
Integer as parameter domains, why would you want to abstract one common
category for it? You must have some more domain parameters in mind.

Ralf

[Neven Sajko]

I ended up fixing this issue by moving the rat_fun_var_tran function
from the Spad package to an Input file.

I think this code has the potential to be actually useful to other
people, so I'll mention it again once I have usage examples ready.

Neven