DIP 50 - AST macros

[Walter Bright]

On 11/13/2013 1:08 AM, Don wrote:
> On Wednesday, 13 November 2013 at 08:45:13 UTC, Walter Bright wrote:
>> On 11/13/2013 12:03 AM, Jacob Carlborg wrote:
>>> Again, operator overloading in D is too limiting to implement something Linq
>>> like.
>>
>> Ok, let's set aside the opEquals and opCmp issue for the moment.
>>
>> Can AST macros do anything that expression templates cannot?
>
> With an expression template you still can't create a statement. It has to
> revolve to a declaration.

Actually, there is a way to do this. I wrote an article years back on how to 
write "statement" workalikes using lazy function parameters. I suppose I should 
dig that up if I can find it.


> But as I said before, it's primarily syntax sugar. Expression templates are just
> a mass of boilerplate code. I came to the conclusion that the code for
> expression templates was no less ugly than for string mixins.
>
> What is true, though, is everything an AST macro can do, can already be done
> with a string mixin. The syntax is just ugly.
>
>                   calling syntax power  implementation
> string mixin       ugly         high      ugly
> expr template       ok          low       ugly
> AST macro          good          ?         ?

This implies to me that we ought to explore the limits of expression templates, 
which already exist, in preference to creating a wholesale new feature.