AST Macros about gmqcc HOT 4 OPEN

Might be good do note that when they are AST macros and you don't actually use a {{{body}}} in there, then the following will NOT work:

macro for_stuff(n) { for (float i = 0; i < n; ++i) }
// used as
for_stuff(5) {
    print("Foo\n");
}

because parsing the macro definition itself will give you a parse error about a missing body for the for loop in it.

The nice part about ast macros is that a lot of checking (specifically syntax within the macro definition) will happen while parsing the macro definition, so if there's a syntax error it'll be shown in there. While with the preprocessor macros you'll end up getting an error at each use of the macro, and with huge macros it's hard to find the actual point of failure. Plus, there'll be syntax checking at the macro's use for the actual parameters directly.

It may be good to have the possibility to request a specific type in a macro parameter though. So that for instance the macro can create a counter variable accessible in the body by taking a variable-name as parameter. Note that in the above macro, the i will not be accessible if we have hygienic macros!

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Implementation wise we'd need to add copy-ctors to ast nodes. Which are also required for inlining.
So I'm referencing #35 here.

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I would also like AST macros to return values (e.g. by also adding a syntax like gcc's ({ ... }) construct.

Furthermore, I would really also like a replacement for #ifdef

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Will this work? If yes, why is x in the right scope? If no, why not?

macro do { {{{body}}} }
do { float x; }
do { float foo() { return x; } }

Or would it be better to have a second simple CPP mode that only supports argumentless #define/#undef and #ifdef/#else/#endif?

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