2010/9/9 Andrew Gwozdziewycz <apg...@gmail.com>:
> On Thu, Sep 9, 2010 at 3:48 AM, Laurent PETIT <laurent.pe...@gmail.com> wrote:
>> Hello,
>>
>> 2010/9/9 Sean Corfield <seancorfi...@gmail.com>:
>>> On Wed, Sep 8, 2010 at 7:28 AM, CuppoJava <patrickli_2...@hotmail.com>
>>> wrote:
>>>> I found the easiest way to introduce macros is just to introduce them
>>>> as small syntactic sugaring. For example, getting rid of the explicit
>>>> (fn [] ...) for macros like (with-open file ...).
>>>
>>> Interesting. I don't see any real difference between macros and C
>>> preprocessor stuff and C++ templates at a conceptual level. I think
>>> Clojure macros are much cleaner, but essentially they are similar. So
>>> in the Java world, generics (templates) are not yet widely used
>>> outside the libraries and maybe that's why Java devs find macros hard
>>> to comprehend?
>>
>> I think that even at the conceptual level, the differences are big:
>>
>> a. C/C++ is a "pre-processor". It does a first pass on the code.
>> Only at the end is the C/C++ compiler invoked. In Lisps, there is
>> still this "first pass/second pass" thing, but it's at a waay finer
>> granularity level: the top level form. At the end of the evaluation of
>> each top level form, a new macro may have been defined and can be
>> called immediately by the next top level form. So not only is the
>> "set" of macros not closed in Lisp (and in C/C++, to some extent, it's
>> also not closed, even if rather limited), but it can be expanded
>> during the compilation of the "program".
>
> Of course the real difference is that in Lisp macros you are working
> directly on the AST, where in C/C++ macros you're working at the
> source level. My understanding of the C/C++ preprocessor is that it
> more or less does a string substitution, which *may* lead to a syntax
> errors (you often see #define X(y) do { y } while (0); to get around
> different limitations), or undesired results, not to mention
> unintended variable capture, etc, etc, etc.
>
> The fact that Lisp macros actually operate on the AST means that Lisp
> macros can make *changes* to the AST (insert things, remove things,
> rearrange things), and *not* just substitute FOO for BAR. This is a
> hell of a lot more powerful.
Yeah
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
