Reimplementing the bulk of std.meta iteratively

[Bruce Carneal]

On Wednesday, 30 September 2020 at 23:17:27 UTC, Timon Gehr wrote:
> On 29.09.20 01:37, Stefan Koch wrote:
>> ...
>
> It's not a first-class type if you can't declare a variable of 
> that type. If this does not work, it's not first-class, it's 
> syntax sugar for reification:
>
> type t = int;
> auto f = (t x)=>x;

Can anything computable using just the source as input be 
considered a first class type?

If so, what do we call type variables that can not be?