[Axiom-developer] Re: fixing SPAD

[Gabriel Dos Reis]

On Sat, 19 May 2007, Martin Rubey wrote:

| Dear Gaby & Waldek,
| 
| as you may know, there is a problem fixing bug #354, Complex R is not
| necessarily a field when R is a field.
| 
| It would be quite straightforward to fix it, if we could conditionally export
| Field, depending on a Boolean valued function, like
| 
| if R has Field and R has Finite and size()$R rem 4 = 1 then Field
| 
| Currently, spad seems to accept statements of the form
| 
|    D has C
| 
| and
| 
|    D1 is d2
| 
| only.  (Please check this, I'm not entirely sure.)  Do you think it would be
| difficult to fix this?  I do not see a workaround, unfortunately.


Martin --

   I believe you raise a fundamental problem, which is that Spad
should allow combination of predicate through usual logical operators.

For a given specific case, one might look for a workaround that
simulates type checking at runtime. However, I don't believe that is 
a good way forward:

   (1) that usually leads to unnatual, unmaintainable code in the long run;
   (2) we fail to express directly what our ideas;
   (3) it is not clear we have a coherent systematic approach.

Therefore, I believe this is an issue that should be given thought.

-- Gaby