What are AST Macros?

[Andrei Alexandrescu]

On 07/12/2010 06:21 PM, Nick Sabalausky wrote:
> "Steven Schveighoffer"<schveiguy at yahoo.com>  wrote in message
> news:op.vfq0aydoeav7ka at localhost.localdomain...
>> On Mon, 12 Jul 2010 16:22:28 -0400, bearophile<bearophileHUGS at lycos.com>
>> wrote:
>>
>>> Steven Schveighoffer:
>>>> bearophile:
>>>>> String mixins are a hack, just a bit better than C preprocessor
>>>> (because
>>>>> they are scoped), they are not a replacement of clean macros.
>>>>
>>>> Interesting statement, can you back it up? :)  What can you do with a
>>>> macro that you can't do with a mixin?
>>>
>>> In the meantime others have already given you some answers, I can add
>>> one example. The Brainfuck language allows you to do every kind of
>>> thing, I have seen even compilers written in it, but its usage is very
>>> unhandy, it's bug-prone, requires lot of code to do even simple things,
>>> and it's very hard to modify and debug programs written in it. What I
>>> meant is that string mixins in theory allow you to do many things, but
>>> in practice you can't use them for complex tasks, and you can't modify
>>> and fix the resulting code if you try to use them for more complex
>>> tasks. They are not a long-term solution for a language that seriously
>>> wants to improve over C and its preprocessor macros, they are a hack.
>>
>> Brainfuck is basically a toy example of a language.  Nobody uses it for
>> serious work.  Mixins are much better than a hack, the syntax of using
>> them is just not polished.  They are easy to use/understand because a)
>> people understand the language and b) people understand string
>> manipulation.
>>
>
> But when you're talking about the string being actual code, you're not
> always talking about typical string manipulation, sometimes you're talking
> about parsing which is only "string manipulation" superficially.
>
>>
>> I'll give you another example -- javascript and HTML editing.  Most people
>> would prefer to just use the innerHTML component of an element than have
>> to use the DOM methods to create individual elements and add them as
>> children, etc.
>>
>
> For writing, yes, but there's also reading: How many people do you know who
> would rather find the elements they want by parsing innerHTML instead of
> just dealing with the readily-available tree? None, I would hope, but the
> latter is essentially what we have to do for many of the more advanced
> things that string mixins *technically* replace AST macros for.

But bitfields and other similar code generating samples don't parse - 
they generate.

Andrei