Re: Macros: Scheme vs Common Lisp

Holger> Interestingly there is a difference whether you quote bar or not: Holger> (setq bar 23) Holger> (defmacro foo () 'bar) Holger> (let ((bar 42)) (foo)) => 42 Holger> (defmacro foo () bar) Holger> (let ((bar 42)) (foo)) => 23 Holger> So, you can get the behaviour you want, you just need to know Holger> how ;-) No, this is different. When you don't quote bar, you get the value of the binding at macro *definition time*. I want the value of the binding at macro *use time*. If you do a (setq bar 47) between definition and use, you'll see the difference. MS> I don't understand that last sentence. If I create a package, MS> and I put abstractions in that package, may they be syntactic or MS> semantic abstractions, I want those abstractions to be able to MS> access bindings in the package. Holger> Which is of course possible if you use packages in CL ;-) Yeah, if I use explicit qualification, which amounts to not using the package system at all. MS> Absolutely. I just fucked up the example. In the case of MS> special variables, you do want the macro to refer to the MS> dynamically bound version. Holger> I was under the impression that setq at the toplevel would Holger> automagically be declared special, but obviously this is not true for Holger> (or required by) the current ANSI standard as readable in the Holger> HyperSpec. (CMUCL does this, IIRC, Allegro CL doesn't). So what's the politically correct way to define top-level bindings which are not special in Common Lisp? Holger> PS: What about my second question: is it possible to obtain the CL Holger> behaviour in Scheme ? I'm not sure what exactly you mean. If you mean: "Can I access bindings not within the scope of a macro from the macro?" ... then the answer is no, just as you can't access bindings not within the scope of an abstraction from within the abstraction. You shouldn't be able to. If you want something equivalent to dynamic binding, you generall use lexical scoping plus dynamic assignment in Scheme, in which case the macro will do what you want. -- Cheers =8-} Chipsy Friede, Völkerverständigung und überhaupt blabla