RE: PD datatyping doc plans

> The "pairing" model itself should absolutely be defined as part of
> the MT. It was only the idioms that would be left out of the MT. But
> perhaps the idioms also need to be in the MT, but modularly, as a
> layer on top of the pairing model, so we retain the insulation of
> the core data typing model from changes/evolution of idioms.


A subtly with the P approach is that there isn't just one type, there can be
any number of range constraints. These, in the logicians world, create a
single intersection type, but for the rest of us they look suspiciously
different from one type. Thus P (in some instances) doesn't follow the
elegant pair picture.

The primer level material on PD needs to suppress that complication. I think
viewing the pairing as something that gets discussed in the less formal
section, gets implemented in actual code but is
extended/side-stepped/ignored in the more formal section will probably be
OK.


Jeremy