New syntax for comma expression

[Paul Backus]

On Wednesday, 20 November 2024 at 23:11:37 UTC, Richard (Rikki) 
Andrew Cattermole wrote:
> During semantic analysis, some code gets lowered to the comma 
> expression.
>
> [...]
>
> Proposed grammar:
>
> ```diff
> CommaExpression:
> +   "class" ConstructorArgs|opt AnonBaseClassList|opt 
> AggregateBody
> +   "__commaExpr" '(' CommaExpression ')'
> ```

As a general rule, I don't think we should be adding new syntax 
to D because it's easier for the compiler to generate than the 
existing syntax.

If there's something in D's semantics that the existing syntax 
*can't express*, then there's a discussion to be had. But I don't 
think this qualifies.