Convenient debug printing

[jmh530]

On Friday, 1 February 2019 at 21:40:29 UTC, Meta wrote:
> [snip]
>
> Meaning no offense to Walter, his recent statements on the AST 
> macros makes me think that he is mistaking what Jacob has 
> proposed before (Lisp or Rust-style hygienic AST macros) for 
> C-style text macros (which are, of course, supremely terrible).
>
> His main argument, about not wanting people to be able to 
> invent their own syntax and encourage fragmentation within the 
> language community, does not ring true. All you have to do is 
> look at Rust to see that it is possible to support a limited 
> form of AST macro without any adverse effects.

In general, the rvalue DIP makes pretty clear that Walter and 
Andrei have a high bar for the quality of a DIP, particularly one 
that could have a big impact on the language. I don't think the 
old AST macro DIP is probably up to the standard that would be 
needed at this point regardless. It would need a re-work and 
definitely need to be written from the perspective of convincing 
W&A, which is a pretty high hurdle given their biases.

Two of the interesting things about AST macros to me are 1) that 
it seems pretty straightforward to implement C++'s metaclass 
proposal using them, 2) not only could a lot of D's other 
features like foreach be written in terms of them but a lot of 
the attributes could too. This could enable a lot of 
customization, which could be good or bad...