Program stack overflow defining infix operator

On 8/9/09, Barton Willis <willisb at unk.edu> wrote:

> (1) Should Maxima have distinct simplifying and non-simplifying logical
> connectives? If so, what should we name the new functions.

I'd like to rename the existing, non-simplifying "and" and "or" to
"and_then" and "or_else", and introduce new simplifying operators
"and", "or", and "not".

I;m not opposed to inventing other, simplifying operators
e.g. nand, implies, iff. But let's get the basics in place first.

> (2) Short or non-short circuited?

"and" and "or" should be commutative with no special
evaluation scheme (so all arguments are evaluated unless
quoted). "and_then" and "or_else" should be noncommutative,
with an evaluation scheme to make them short-circuit.
"not" should be simplifying.

> (3) What simplifications should automatically be used? How about optional
> (spendy) simplifications (option variables or special extra simplification
> functions).

Well, I'm inclined to have only some easy simplifications built in,
for some value of "easy"; maybe easy = stuff analogous to
arithmetic simplifications. For the rest, I'd rather have functions,
instead of flags.

> (4) What about non-boolean arguments? (for example:  matrix([7]) and
> [8,9]).

Just leave them be. (It is unmathematical to complain about
unrecognized expressions. Let the user worry whether it is
meaningful or not.)

> (5) What about errors?

It annoys me when simplification functions trigger errors.
I hope we can avoid that.

> (6) What about prederror? Should we keep true / false / unknown logic?

I'd like to cut out prederror and all prederror=true branches.
I think that makes "is" the same as "maybe", incidentally.

I think it's useful to have "unknown", I'd like to keep it.
Although it's just a convenience; if "is" can return something
other than true or false, then member(is(x), [true, false]) or
booleanp(is(x)) or is(x) in {true, false} or featurep(is(x), boolean)
(only the first of those is for real at the moment) could replace it.

Thanks for your work on this topic. I suspect the simplifying
Boolean stuff which you wrote in share already handles some
of these items.

best

Robert Dodier