[Aldor-l] Strange Error Message

[Christian Aistleitner]

Hello Ralf,

On Sat, 27 Jan 2007 00:33:11 +0100, Ralf Hemmecke <ralf at hemmecke.de> wrote:

> Can somebody from the Aldor developers explain how I should understand
> the following error message and what I should do about it.
>
> "tcdistpoly.as", line 50:         assertEquals(T, t1/t2, t2*t1);
>                            ..........................^
> [L50 C27] #1 (Error) No one possible return type satisfies the context  
> type.
>    These possible return types were rejected:
>            -- SparseIndexedPowerProduct(MachineInteger, MachineInteger)
> The following could be suitable if imported:
>    /: (SparseIndexedPowerProduct(MachineInteger, MachineInteger),
> SparseIndexedPowerProduct(MachineInteger, MachineInteger)) ->
> SparseIndexedPowerProduct(MachineInteger, MachineInteger) from
> SparseIndexedPowerProduct(MachineInteger, MachineInteger), if
> SparseIndexedPowerProduct(MachineInteger, MachineInteger) has  with /:
> (%, %) -> %
>
> [...]
>
> What can I do? Please help.

once again, the Aldor compiler is not smart enough to resolve the  
conditional exports correctly. The problematic thing is the export of the  
/ function.

As I do not think the Aldor people will give a fix in reasonable time, I  
would suggest to tell Aldor again that T has a function /. For me, the  
following piece of code worked (note that I changed t2*t1 to t2/t1 as I do  
not know what conditions you pose on multiplication):

   assertTrue( T has with { /: (%, %) -> %; } );
   if T has with {/: (%, %) -> %;} then {
     assertEquals(T, (t1/t2)@T, (t2/t1)@T);
   } else {
     never;
   }

Abstracting the above piece of code into a macro leaves you with a clean,  
smooth and maintainable test case.

Kind regards,
Christian