[Axiom-mail] Dynamically constructed return types

[Marcus Better]

Hi all,

I got stuck trying to write a spad function that will take an argument 
of a certain type T, construct from this some other type S, and return 
an object of type S. I am using the "Any" type to do this, but I have a 
problem extracting and using the type and object encapsulated in the Any 
object.

Here is a simplified example (yes, Laurent series again!): The function 
f takes a univariate Laurent series over the domain K, performs some 
calculation, constructs a domain L which is a SimpleAlgebraicExtension 
of K (whose defining equation depends on the computed values). The 
function then returns some other Laurent series over L.

This is some sample code. (It is not tested, I just removed the 
irrelevant parts of my code.)

----------------------------------------------------------------
)abbrev package FOO Foo
Foo(K: CommutativeRing, ULS: UnivariateLaurentSeriesCategory K):
  Exports == Implementation where

  Exports ==> with
    f: ULS -> Any

  Implementation ==>
    f(x) ==
      -- Compute some equation over K.
      eq := monomial(1,2)$SUP(K) _
            - monomial(first coefficients taylorRep x, 0)$SUP(K)

      -- Create an extension L of K.
      L := SimpleAlgebraicExtension(K, SUP K, eq)

      -- Create and return a new Laurent series over L.
      -- The 'zero' variable is necessary due to a compiler bug...
      zero := 0::L
      TS := UnivariateTaylorSeries(L,z,zero)
      LS := UnivariateLaurentSeries(L,z,zero)
      y := map(#1::L, coefficients taylorRep x)$StreamFunctions2(K,L)
      coerce(laurent(-2, series(y)$TS)$LS)$AnyFunctions1(LS)
----------------------------------------------------------------------

Now, how can the caller of f retrieve the domain L and, say, extract the 
first coefficient of the returned series y?

Regards,

Marcus

PS. Please CC me with any replies, I am not subscribed to the mailing lists.

--
-----------------------------------------------------------------
Marcus Better
Department of Mathematics                      Tel. +46 8 164539
Stockholm University                           Fax +46 8 6126717
SE-106 91 Stockholm
Sweden                                     http://www.math.su.se
-----------------------------------------------------------------