On 07/12/2010 03:22 PM, bearophile 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.
In my opinion the std.bitmanip.bitfields souce code is already past
the decency limit for string mixins, and I hope they will be replaced
by something better.
Clearly a more structured approach would be better. On the other hand
bitfields is literally the first code-generating tool I ever wrote, so I
expect better idiomatic code will come about after the community's
experience increases.
I don't agree with Andrei when he says that CLisp macros (and even
more Scheme macros that are hygienic too) are as hairy and
unmantenable as code that uses string mixins heavily.
I said:
=======
Though I sympathise with all of the above, I should add that I have
looked at languages that feature AST macros (Lisp, Scheme, Dylan) and
such macros are difficult to create and read as well. We're not looking
at day and night improvement there.
=======
and you claim, quite unequivocally, that I said:
=======
CLisp macros (and even more Scheme macros that are hygienic too) are as
hairy and unmaintainable as code that uses string mixins heavily.
=======
I mean WTF?
Back on topic: http://www.apl.jhu.edu/~hall/Lisp-Notes/Macros.html.
Compare the simple macro in the beginning and the correct macro at the end.
Andrei
