This should be an FAQ because we have discussed it several times :-)
The short answer is that, in all flavours of AXIOM, if you assign to Rep
then you are asking for implicit coercions between % and Rep -- and that
can lead to unfunny situations as above.
The proper way is to define Rep as a constant, i.e. Rep == X.
Oh, I thought, that just OpenAxiom changed it to using "Rep==X". If I
understood correctly, in FriCAS "==" does not mean constant definition
but rather "delayed assignment".
>grep '^[ \t]*Rep *:=' *|wc -l
239
>grep '^[ \t]*Rep *==' *
ffrac.as.pamphlet: Rep == Record(num : X, den : X) ; -- representation
herm.as.pamphlet: Rep ==> Vector R;
interval.as.pamphlet: Rep ==> Record(Inf:R, Sup:R);
newdata.spad.pamphlet: Rep ==> VTB
newdata.spad.pamphlet: Rep ==> A
newpoly.spad.pamphlet: Rep ==> List Term
regset.spad.pamphlet: Rep ==> LP
sregset.spad.pamphlet: Rep ==> LP
triset.spad.pamphlet: Rep ==> LP
triset.spad.pamphlet: Rep ==> LP
So in the FriCAS sources, there is only *one* instance with ==. And
interestingly, this is not SPAD, but an Aldor program.
So I assume, in FriCAS, I will rather have to use ==> instead of ==.
I've tried both, and for ==> as well as for ==, I can do without $X.
Waldek, what would you suggest? I definitely want rep and per. Would be
good, if they were defined automatically, but for the moment I can live
with defining them myself. Using rep and per just helps me to keep track
of the difference between % and Rep. Automatic coercion should not be
done for SPAD programs, not even between % and Rep.
Ralf
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