Hi Zach, you might want to look at this paper explaining how to write a correct macroexpand-all (which requires a code walker) in Common Lisp: http://www.merl.com/publications/TR1993-017/
The compiler certainly has to do something like that, but might not do all of the macroexpansion before starting any compilation as Konrad explained. What the compiler needs to do is track the lexical environment while walking down the source forms. When a code walker wants to introduce additional bindings, such as macrolet (for local macros) or symbol-macrolet (for new symbols) it needs to be able to extend the environment accordingly. So, you either have to access the compiler internals, especially its environment handling, or track the environment yourself (as Konrad suggested). As an aside: The problem in Common Lisp is mainly that the environment handling is not exposed in the standard, thus you cannot write a portable code walker without doing some environment handling yourself. You might also want to look at core.async, which uses a code walker to transform go blocks into state machines. I have not (yet) checked its restrictions (someone told me, that it cannot even look into anonymous fn forms within its body!), but it is generally very hard to write a code walker that can handle all special forms (in Common Lisp I don't know any). +10 for having a library that supports writing correct and (almost) complete code walkers Best, Nils On Thursday, September 5, 2013 12:09:28 PM UTC+2, Konrad Hinsen wrote: > > Zach Tellman writes: > > > I guess I'm confused, then. You contrast "complete recursive > > expansion" with what the compiler does, and then say it's recursive > > prewalk expansion, which is exactly what the compiler does. Can > > you clarify the difference between what you're doing and what the > > compiler does? > > Here's an example: > > (defmacro foo [x] > `(list ~x ~x)) > > (defmacro bar [x] > `[~x ~x]) > > Now let's work on the form > > (foo (bar 'baz)) > > Plain macroexpand returns > > (list (bar 'baz) (bar 'baz)) > > whereas tools.macro/mexpand-all gives > > (list ['baz 'baz] ['baz 'baz]) > > It does this by first calling macroexpand, so foo gets called exactly > as during Clojure compilation and returns > > (list (bar 'baz) (bar 'baz)) > > mexpand-all then goes through that form and expands the two subforms > (bar 'baz). > > So mexpand-all does exactly what the compiler does, in particular it > calls the macros with exactly the same arguments. But the compiler > interleaves macro expansion with compilation, so it never gives you > access to the fully expanded but uncompiled form which is > > (list ['baz 'baz] ['baz 'baz]) > > Konrad > -- -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
