mixin + CTFE, to big a hammer??

[Andrei Alexandrescu (See Website For Email)]

Mikola Lysenko wrote:
> Andrei Alexandrescu (See Website For Email) Wrote:
>> Syntactic manipulation will be in D, too. The thing is, it only
>> works for manipulating D code, not DSLs that don't, and can't, look
>> like D (e.g. regex, SQL, automata, etc.). So we will have syntactic
>> (AST-level) manipulation for D forms, and string manipulation for
>> non-D DSLs. It's all fine. It's understandable that people who
>> _only_ see the string manipulation stuff without the vision behind
>> it will immediately point to its limitations. So let's give it a
>> few months and you won't be disappointed :o).
>> 
>> 
>> Andrei
> 
> I guess it wouldn't hurt to wait and see what happens next.  I just
> hope that we don't end up going so far with the experiment, only to
> find that it is a dead end.  MixinStatement is a radical departure
> from the previous meta programming constructs in D, and it needs to
> be carefully balanced.  I'm all for extending and improving the scope
> of the language, and I expect we will continue to see new and radical
> improvements to the compile time code manipulation facilities.
> 
> However, it just feels like string mixins have been uncritically
> accepted into the language, with very little thought paid to the
> consequences - let alone the possibility that there might even exist
> better alternatives.  I think the situation right now calls for some
> cautious reappraisal of what benefit mixins add over traditional
> approaches, and whether there might be a simpler solution.
> 
> I think we can get automata, regexes and SQL expressions without
> adding direct source code manipulation.  The key limitiation string
> mixins address is name generation.  Right now you can't use a
> template meta program without string mixins to generate, say a member
> name for each field in a SQL query.  If we could figure out some way
> to solve this problem without direct text preprocessing, I would
> personally feel less ill at ease.  I certainly suspect it is
> possible.

It will be possible once AST manipulation makes it into the language. 
That, not now, will be the proper time for the cautious reappraisal. 
Even then, if certain idioms will remain much easier with strings vs. 
ASTs, there might be significant pressure to keep the feature.


Andrei