Bill Page wrote:
>
> On 14 November 2016 at 23:59, oldk1331 <[email protected]> wrote:
> >> How about using List of EXPR as Rep?
> >
> > Second thought, it will not work, polynomial will still be expanded.
> >
> >> On the other hand, probably carrying it too far, one might use OutputForm
> >> which
> >> is very expressive and greatest possible "symbolic", if only there were a
> >> way
> >> back ;)
> >
> > Yes, something between OutputForm and Expression: it will keep the
> > similarity
> > of its input form and have semantic to perform various operations.
> >
>
> InputForm is rather poorly named but logically I think it does fall
> somewhere between OutputForm and Expression. Both InputForm and
> OutputForm are represented as Lisp SExpressions
No. Both InputForm and OutputForm are represented by SExpression.
Now, compound SExpression is a list of SExpressions, but at the end
you will get atoms.
> and functionally
> assisted by built-in boot and Lisp coding. In fact the current
> version of 'Symbolic' takes advantage of the fact that for the most
> part InputForm can just be interpreted as a particular sort of
> OutputForm via 'pretend'.
That is bad. There are good reasons to change representation
of OutputForm, but we can not currently do it because code
making unwarranted assumptions like this would get broken.
> This is adequate in a large majority of
> cases but it is awkward for example in representing arbitrary
> precision Float numbers. Conversion of Float to InputForm relegates
> this to the syntax of a function call to 'float'. As I understand it
> the formatting of Float values is currently handled directly by coerce
> in Float while DoubleFloat is handled by OutputForm. In principle
> OutputForm could be improved to do both.
Actually, DoubleFloat formatting is handled by coerce in
DoubleFloat. Doubles as elements of OutputForm are probably
still tolerated, but eventually all such uses should be
eliminated.
More generally, this is question of what is allowed set of
atoms in SExpression and in OutputForm. Currently doubles
are allowed as atoms (because they are available in Lisp
and we can reuse Lisp support). However, domain semantics
affects desired output, so all data should go trough
"coerce(x : %) : OutputForm". OutputForm can do something,
but that should be limited to some general formatting
decisions. For this we may need new atoms or nodes
(to carry extra formatting information).
--
Waldek Hebisch
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