New syntax for string mixins

[Jacob Carlborg]

On 2010-12-15 08:57, Don wrote:
> Jacob Carlborg wrote:
>> On 2010-12-14 13:05, Don wrote:
>>> Graham St Jack wrote:
>>>> On 14/12/10 20:33, Vladimir Panteleev wrote:
>>>>> On Tue, 14 Dec 2010 09:30:46 +0200, Graham St Jack
>>>>> <Graham.StJack at internode.on.net> wrote:
>>>>>
>>>>>> There is of course the worry that it could get so easy that everyone
>>>>>> starts doing it, and we have (relatively) impenetrable code
>>>>>> everywhere
>>>>>> instead of just deep in the bowels of framework libraries.
>>>>>
>>>>> TBH, I'm more excited by AST macros which I understood are planned for
>>>>> D3, as mentioned here:
>>>>> http://s3.amazonaws.com/dconf2007/WalterAndrei.pdf
>>>>> They seem to promise the power of mixins, but without the mess.
>>>>>
>>>>
>>>> I took a look at the pdf, but couldn't see how the AST macros could
>>>> come
>>>> close to the kinds of things that are possible (but difficult) with
>>>> mixins.
>>>
>>> That fact was recognized at the conference, on the following day. As a
>>> result, AST macros were dropped from D2.
>>
>> Do you have an example that would work with string mixins but not with
>> AST macros?
>
> Well, it's a bit hard without a formal definition of AST macros.
> But the stuff I talked about at the conference, I have no idea how to do
> with AST macros.
>
> There's code like this, which generates an asm instruction.
>
> ------
> mixin( opToSSE[operations[done+1]] ~ suffix ~ " " ~ XMM(numOnStack-1) ~
> ", " ~ indexedSSEVector(ranklist, operations[done], vectorsize));
> -------
>
> using the functions:
> ============
> const char [][5] vectorRegister = ["ECX", "EDX", "EBX", "ESI", "EDI"];
>
> char [] indexedSSEVector(char [] ranklist, char var, char [] vecsize)
> {
> return "[" ~ vectorRegister[vectorNum(ranklist, var)] ~ " + " ~ vecsize
> ~"*EAX]";
> }
>
> char [] XMM(int k) { return "XMM"~ itoa(k); }
>
> char [][char] opToSSE() {
> return ['*':"mulp"[], '+': "addp", '-': "subp", '/': "divp"]; }
>
> int vectorNum(char [] ranklist, char var)
> {
> int numVecs=0;
> for (int i=0; i<var-'A'; ++i) {
> if (ranklist[i]=='1') ++numVecs;
> }
> return numVecs;
> }
> ============

I can't quite visualize how the final code will look like and as you say 
it's hard without a formal definition of AST macros. But I think somehow 
it would be possible, I mean instead of combining strings one combine 
expressions/syntax. But I don't know if it would be possible to combine 
incomplete expressions.

>>> They need to roughly match string mixins in power. At this stage, there
>>> is no proposal for how they should work.
>>
>> I think someone, Nick Sabalausky perhaps, suggested to have something
>> like the hygiene macros in Nemerle:
>> http://nemerle.org/wiki/index.php?title=Macros
>
>  From an implementation point of view, the differences between Nemerle
> macros and string mixins are mostly syntactic.
> The one thing about them that I find really impressive is the IDE
> integration, especially that they got syntax highlighting to work. I
> don't know they've done that.

As far as I can see the content of a macro in Nemerle is just code. But 
if you're referring to the syntax expression/statement which adds new 
syntax to the language then I agree.

-- 
/Jacob Carlborg