In OpenAxiom functions can return domain-values. This works for example in

MyPair(X:Domain,Y:Domain):Domain == Record(p1:X,p2:Y)

   Function declaration MyPair : (Domain,Domain) -> Domain has been
      added to workspace.

MyPair(Integer,Float)

   Cannot compile the declaration for p1 because its (possible partial)
      type contains a local variable.
   OpenAxiom will attempt to step through and interpret the code.

Compiling function MyPair with type (Domain,Domain) -> Domain 
   Compiled code for MyPair has been cleared.

(1)

where Record is a built-in type.

But I cannot use a compiled type such as Product in place of Record

MyPair2(X:Domain,Y:Domain):Domain == Product(X,Y)

   Function declaration MyPair2 : (Domain,Domain) -> Domain has been
      added to workspace.

MyPair2(Integer,Float)

   Product(#1,#2) is not a valid type.

Product(Integer,Float)

(2)