DIP 50 - AST macros

[Jacob Carlborg]

On 2013-11-11 12:34, Dmitry Olshansky wrote:

> I have to say I like it.

Cool :)

> I find it nice that it would allow one to finally ensure that inlining
> is always done by making critical primitives macros instead of
> functions. This is vastly superior compared to the _only_ current option
> of generating unrolled code with string mixins.
>
> I'd call attribute macros - declaration macros in line with statement
> macros, then describe how they look - a lot like attributes.

Ok, I can change that.

> Things to note though:
>   - Can't implement scope(exit/success/failure) because that would need
> to capture the outer scope to pack it into try/catch/finally.

Right. scope(exit) could perhaps be implement with a custom struct and 
calling a block in the destructor.

>   - Can't implement foreach if only because of the syntax of the latter.

I would think something like this:

macro foreach (T) (Context context, Ast!(Symbol) var, Ast!(T) 
collection, Statement block)
{
     if (isRange(collection))
     {
         return <[
             for (auto __r = $collection; !__r.empty; __r.popFront())
             {
                 auto $var = __r.front;
                 block;
             }
         ]>;
     }

     else if (hasOpApply(collection))
     {
         ...
     }

     else ...
}

Perhaps not all of the existing syntax can fit in a macro.

>   - There is no definition of Ast!(T) construct - I take it's a struct
> or a class of sorts and the whole thing works with the CTFE engine. Then
> it also needs specification of Statements, Declarations.

Yes, something like that. I don't know exactly how the Ast type need to 
look like. See one of my replies to bearophile:

http://forum.dlang.org/thread/l5otb1$1dhi$1@digitalmars.com

>   - It seems like I can use AST literal in R-T code as well? That would
> be useful but only if some library actually accepted these AST nodes.

Actually, I haven't thought about this. I think my original idea was 
that <[ ]> should only work inside macros. But that it would be possible 
to pass Ast nodes to other functions.

-- 
/Jacob Carlborg