[m-dev.] subtypes proposal

[Peter Wang]

On Thu, 14 Jan 2021 12:55:39 +1100 Peter Wang <novalazy at gmail.com> wrote:
> Hi,
> 
> In this proposal, subtypes are distinct d.u. types that share a data
> representation with a base type, which is a normal d.u. type.
> Subtypes of subtypes are allowed.
> Every term of a given subtype must also be valid term in the supertype
> (recursively, up to the base type), with the same data representation.
> 
> A subtype can be introduced like this:
> 
>     :- type SUBTYPE =< SUPERTYPE
>         --->    BODY.

Subtypes are supported as of ROTD 2021-04-14.

Peter