Proposal: First class types (at compiletime)

[Stefan Koch]

On Friday, 21 July 2023 at 11:53:23 UTC, Commander Zot wrote:
> On Thursday, 20 July 2023 at 21:09:40 UTC, Paul Backus wrote:
>> On Thursday, 20 July 2023 at 17:52:38 UTC, TheGag96 wrote:
>>> On Thursday, 20 July 2023 at 16:57:16 UTC, jmh530 wrote:
>>>> You mean dropping it was a mistake? Or you mean type 
>>>> functions are a mistake? (if so, can you explain more what 
>>>> those languages had an issue with)
>>>
>>> Sorry, I was probably unclear - not going the type functions 
>>> route was a mistake.
>>
>> The thing is, none of the existing template stuff is ever 
>> going away. So the choice is not really between "templates" 
>> and "first-class types", it's between "templates" and "both".
>>
>> I agree that, in retrospect, relying on templates for 
>> metaprogramming was probably a mistake. But at this point, 
>> there's nothing we can do to fix it short of starting a new 
>> language from scratch--which is not something the D leadership 
>> has any interest in.
>
> but without having them, we still have to write recursive 
> template metaprogramming for things that would be expressed 
> better with normal functions.
> yes, it wouldn't remove old code, but it would be a huge win 
> for any new code in my opinion.
> and I remember walter mention CTFE for calculations as a huge 
> win, so i'm really not sure if this wouldn't be either. which 
> is the point why I bring up the topic.

I can share the latest state of type-functions before I abandoned 
the approach.
I believe this is close to what I ended up wtih:
https://github.com/dlang/dmd/compare/master...UplinkCoder:dmd:talias_master
as you can see it's quite a bit of code and it leads to strange 
interactions with the type system.
At the time I thought that's inherent and cannot be fixed, and 
indeed if you want to keep the same syntax that you are used to 
using in templates, this may very well be the case.
However if you are willing to accept changes to your code, it 
might be possible to do something like this.