No household is perfect

[Chris Cain]

On Thursday, 5 December 2013 at 15:59:08 UTC, Don wrote:
> 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).

I see. I thought you were saying the concept of not having to 
rewrite the D compiler was negligible. Which, of course, is 
false. The speed advantage is but that's really just a minor 
thing ultimately.

> 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.

Hopefully it'll get us to where we need to go.

> But I don't see the point of it being identical to D.

It doesn't _need_ to be, strictly speaking. But having a program 
written in C, some C++, D, SQL, and some CompileTimeScripting 
Language is inherently more difficult to deal with than something 
that limits it to C, C++, and mostly D (that generates necessary 
SQL and fulfills the requirements needed by the CTS-L). 
Considering the CTS-L would be unique to D (and possibly even to 
your project), that's quite an advantage.

> 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.

Why would it have to be? Don't conflate this with the concept of 
"equivalent to a turing machine". We're not getting it because 
it'd be possible to change the meaning of 1+1 to 3. If it were 
more limited ("less powerful") then it would be something that 
wouldn't have been rejected but, potentially, far less useful.