Beyond the veil: What's after type functions

[Paul Backus]

On Wednesday, 6 January 2021 at 16:34:14 UTC, Ola Fosheim Grøstad 
wrote:
> On Wednesday, 6 January 2021 at 16:30:25 UTC, Jacob Carlborg 
> wrote:
>> On 2021-01-04 20:30, Stefan Koch wrote:
>>
>>> With this in mind, please tell me what you think :)
>>
>> I think this looks like yet another new set of features just 
>> to avoid AST macros. What everyone is currently doing is 
>> inventing many highly specialized features just in the name of 
>> avoiding AST macros, regardless of the cost.
>
>
> But the DMD AST model isn't really suitable for exposure. So 
> you would need to design a completely new AST... not sure if 
> this is feasible in this decade? :)

You don't need a stable AST API for AST macros, you just need 
quasi-quoting and unquoting, à la Common Lisp. There's an old 
talk by Walter and Andrei that includes a sketch of what AST 
macros might look like in D [1], which contains the following 
example:

     macro foo(e) { e = 3; }

In Common Lisp, the equivalent would be

    (defmacro foo (e) `(setf ,e 3))

You will notice that nowhere in either example is the AST exposed 
directly.

[1] https://www.youtube.com/watch?v=FRfTk44nuWE&t=1h5m37s