No household is perfect

[Don]

On Thursday, 5 December 2013 at 14:18:46 UTC, Chris Cain wrote:
> On Thursday, 5 December 2013 at 09:25:30 UTC, Don wrote:
>> I think that is of negligible benefit. There's not a whole of 
>> difference between manipulating an AST, vs manipulating text, 
>> and I'm confident that the time taken to do that is always 
>> going to be far more than the time required to lex and parse 
>> text.
>>
>> What AST macros could provide is syntax sugar.
>> But IMHO there's a lot more to be gained from improvements to 
>> compile time reflection.
>
> Negligible? AST macros write the front-end of a D compiler for 
> a string mixin for you. That's not negligible.

What I said was negligible was:
>> "The advantage of AST macros is that the compiler doesn't need 
>> to re-lex and re-parse the result."

It's a negligible benefit because most of the time is spent in 
the semantic pass (which can take unbounded time), not in the 
lexing and parsing steps (which always take time O(n), where n is 
the length of the source code).

> Even if the D frontend was static and didn't change it would be 
> difficult to reach parity. The best that can be done now is a 
> language that reminds you of D (or a D subset that, at best, 
> will confuse users since it's not going to support nearly 
> everything).

Actually everything can be done in a library. Especially when we 
switch to the frontend written in D, the library and compiler 
source can be the same.
But I don't see the point of it being identical to D.

> Of course, I know we're not going to get AST macros, but at 
> least don't say things like it's "negligible". The only reason 
> we aren't getting AST macros is because it's the opposite of 
> negligible; it's _too powerful_.

Remember that it would have to be "more powerful" than an 
arbitrary chunk of source code text. I don't see how that could 
possibly be true.