toExternalString for nonreal RR objects

[d-torrance]

The following behavior of toExternalString isn't quite right:

i1 : x = numeric infinity

o1 = infinity

o1 : RR (of precision 53)

i2 : toExternalString oo

o2 = infinity

i3 : value oo

o3 = infinity

o3 : InfiniteNumber

i4 : x = numeric indeterminate

o4 = NotANumber

o4 : RR (of precision 53)

i5 : toExternalString oo

o5 = NotANumber

i6 : value oo

o6 = NotANumber

o6 : Symbol

Ideally, value @@ toExternalString should act like identity, and in both cases, we're ending up with instances of a completely different class!

To solve this, we:

• Introduce NotANumber, a new instance of IndeterminateNumber.
• Introduce the Number_ZZ syntactic sugar for numeric.
• Modify toExternalString to take advantage of these changes.

So now we have:

i1 : toExternalString numeric infinity

o1 = infinity_53

i2 : value oo

o2 = infinity

o2 : RR (of precision 53)

i3 : toExternalString numeric indeterminate

o3 = NotANumber_53

i4 : value oo

o4 = NotANumber

o4 : RR (of precision 53)

This is a draft for now since there are conflicts with #3630 and I should add tests and docs.

[d-torrance]

I scrapped the Number_ZZ synonym for numeric and changed this to just use numeric(...) in the output of toExternalString for these cases. Also NotANumber is now just a synonym for indeterminate rather than a distinct object.

I also noticed that we weren't consistent for how we dealt with these things in CC. If the real or imaginary part was infinity or nan, we did all sorts of different things:

i1 : toExternalString toCC numeric infinity

o1 = toCC(infinity,.0p53)

i2 : toExternalString toCC(numeric infinity, 5.0)

o2 = toCC(infinity,infinity)

i3 : toExternalString toCC(53, numeric infinity, 5)

o3 = toCC(infinity,.5p53e1)

i4 : toExternalString toCC numeric indeterminate

o4 = toCC(NotANumber,.0p53)

i5 : toExternalString toCC(numeric indeterminate, 5.0)

o5 = toCC(NotANumber,NotANumber)

i6 : toExternalString toCC(53, numeric indeterminate, 5)

o6 = toCC(NotANumber,.5p53e1)

Now we're consistent:

i1 : toExternalString toCC numeric infinity

o1 = toCC(numeric(53, infinity),numeric(53, infinity))

i2 : toExternalString toCC(numeric infinity, 5.0)

o2 = toCC(numeric(53, infinity),numeric(53, infinity))

i3 : toExternalString toCC(53, numeric infinity, 5)

o3 = toCC(numeric(53, infinity),numeric(53, infinity))

i4 : toExternalString toCC numeric indeterminate

o4 = toCC(numeric(53, NotANumber),numeric(53, NotANumber))

i5 : toExternalString toCC(numeric indeterminate, 5.0)

o5 = toCC(numeric(53, NotANumber),numeric(53, NotANumber))

i6 : toExternalString toCC(53, numeric indeterminate, 5)

o6 = toCC(numeric(53, NotANumber),numeric(53, NotANumber))

[pzinn]

sorry I just noticed this PR. I will take a look now. (usual rant, why don't I get notified when a review is requested of me?)