On Thu, Sep 9, 2010 at 10:04 AM, ajuc <aju...@gmail.com> wrote: > > > On 9 Wrz, 14:25, Andrew Gwozdziewycz <apg...@gmail.com> wrote: >> 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. >> >> --http://www.apgwoz.com > > To be fair to C and C++ they allow changing AST: > > #define UNLESS(x,y) {if (!(x)) {y;} }; > > This macro changes (UNLESS x y) to (if (not x) y) - this is different > AST trees. > > The only difference I see is that in C you have to work with > characters, when in lisp you work with lists, and that in C you can > only use preprocessor directives at compile time (you can't output > diffrent code in macro depending on the structure of its arguments), > when in lisp you can use lisp at compile time to change what code will > be created by macro.
Well, C preprocessor macros don't really *change* the AST, it *affects* the source *before* it's passed to the compiler (the compiler creates the AST). You've also stumbled on the most important difference between the two types--those differences make Lisp style macros far more powerful. -- http://www.apgwoz.com -- 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
