Let Over Lambda by Hoyte contains a very lucidly well-written discussion of quotation levels in macros. It also includes a pretty useful technique for being explicit about variable capture. The code is in Common Lisp, but will mostly only differ syntactically from the Clojure code (for the basic example, I mean). There is one non- trivial difference to implement for use in Clojure, which is that Lisp-1 versus Lisp-2 requires being concerned about capture of function names as well, but as indicated in the text this is a simple modification to make.
On Aug 11, 1:21 pm, Rock <rocco.ro...@gmail.com> wrote: > For nested backquotes, Paul Graham in ANSI Common Lisp gives the > clearest explanation. He makes it look almost trivial. As a matter of > fact, once you get the hang of it, it's not at all that complicated. > > I've pretty much verified that what he says concerning CL backquotes > applies perfectly to Clojure as well. The only difference is that you > have to remember that in Clojure, backquotes can *resolve* unqualified > symbols too (which is actually powerful and cool). So no problem > there. > > Rock > > On Aug 11, 6:00 pm, Jonathan Smith <jonathansmith...@gmail.com> wrote: > > > For the sake of contradicting myself, in this paper Alan Bawden > > explains quasi-quote much better than I can. > > >https://eprints.kfupm.edu.sa/60346/1/60346.pdf > > > Note the explanation towards the end of defmacro and constructs such > > as ',' (in clojure I believe it would be '~' ) > > > Also note that Clojure has the added wrinkle of namespace > > qualification. > > > On Aug 11, 1:31 am, Jonathan Smith <jonathansmith...@gmail.com> wrote: > > > > On Aug 10, 3:20 pm, Dragan Djuric <draga...@gmail.com> wrote: > > > > > For example: > > > > > (defmacro creator [param] > > > > `(defmacro created [p] `(the code...)) ;; note the nested quote... > > > > how to resolve that? any examples? > > > > Although I wouldn't cite my own code as a necessarily *good* or easy > > > to understand example, I'll pimp it anyway as it is written and > > > already on the net... > > > >http://github.com/JonathanSmith/CRIB/blob/89a3f4d9c797ef6f4e4f456001f... > > > > A macro is exactly the same as a function, except it has special > > > evaluation rules. > > > You'll notice that in what I posted, I only use defmacro once, > > > everything else is a function that returns a list > > > > (I've found that this gives me extra flexibility later on when I want > > > to continue extending the macro-metaphor... (or if I happen to want to > > > do runtime definition of certain things, I can swap out the macro for > > > a function call and an 'eval')). > > > > You'll also notice that syntax quote qualifies every symbol that it is > > > passed. > > > Your particular example wouldn't work, because you can't define a name- > > > space qualified symbol. There are two ways that you could circumvent > > > this. > > > 1.) use regular old list > > > (list 'defmacro 'created ['p] `(code ...)) > > > > 2a.) Escape and quote certain things: > > > > `(defmacro ~'created [p#] `(code goes here..)) > > > > or > > > > 2b.) `(defmacro ~'created [p#] ~(fn-that-returns-your-code p# and > > > probably some args and stuff)) > > > > or > > > > 2c.) > > > (let [fn-that-generates-expansion > > > (code-to-generate-a-fn-that-generates-an-expansion)] > > > `(defmacro ~'created [p#] (~fn-that-generates-expansion p#))) > > > > You don't actually need to use nested backquote* (For anything**, > > > AFAIK), I tend to avoid it because I think it makes the code fairly > > > unreadable (yes, more unreadable than what I posted). I normally use a > > > helper function and pass the arguments (similar to a foo and foo-1 > > > function when doing recursion). > > > > --------------------- > > > * backquote == syntaxquote > > > > ** I think I used nested backquotes one time in common lisp for > > > something, but I can't remember *why* it was necessary, in particular. > > > I think it is the case where you want to pass a symbol from one macro- > > > environment to the next, say generating a bunch of accessors... --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
