Which language constructs could be done as a library if we accept some breaking changes?

[Paul Backus]

On Thursday, 2 December 2021 at 09:20:26 UTC, Ola Fosheim Grøstad 
wrote:
> On Thursday, 2 December 2021 at 00:58:38 UTC, 12345swordy wrote:
>> On Wednesday, 1 December 2021 at 15:09:28 UTC, Ola Fosheim 
>> Grøstad wrote:
>>> On Wednesday, 1 December 2021 at 15:01:10 UTC, 12345swordy 
>>> wrote:
>>>> What you basically are asking for is C with ast macros.
>>>
>>> Can you emulate D as C with AST macros?
>>
>> https://github.com/eudoxia0/cmacro
>
> That would be a different language. Templates are related to 
> AST macros, but they are limited to expanding on"!".

The syntax used for macro expansion is a trivial detail. Rust has 
"real" AST macros, and they also use `!` for expansion (`vec!`, 
`println!`, etc.).

The biggest difference between AST macros and templates is that 
expanding a template both *generates* code and *binds* that code 
to a symbol in a particular scope.