Hi, > because the symbol's namespace is then nil, and you still can't tell if > they're shadowing it with a let binding, or have renamed it with :as. >
If the namespace is nil then its either been :used or :required. You could check ns-refers to see if its been :used. If its been shadowed the symbol will appear in &env. But, as you suggested, checking for the var may be easier and sufficient as well. That said, neither method is really composable. If the symbol usually represents a normal function, the user may wrap it in a helper or otherwise use it in a way that the symbol is not visible. In that case a macro will never be able to find it. It may be easier (for the implementor and consumers) to make it a special form, like recur when used in a loop or function body. YMMV. - Andy On Tuesday 03 August 2010 23:39:46 Kyle Schaffrick wrote: > On Mon, 2 Aug 2010 07:23:12 -0400 > > Andrew Boekhoff <boekho...@gmail.com> wrote: > > On Sunday 01 August 2010 21:34:16 Kyle Schaffrick wrote: > > > Hello, > > > > > > I'm trying to write a library with two main parts. The first is a > > > macro, I'll call it 'with-feature, that walks through forms passed > > > inside it, and any time it sees a call to another function in my > > > library, 'feature, do some transformations. > > > > > > The problem I'm concerned about is as follows: When my macro sees > > > the forms that are passed into it, the symbols come in however the > > > consumer of the library wrote them. So say I :require my library and > > > alias it to 'mylib', then the call 'with-feature is looking for > > > appears as 'mylib/feature. Or, I could :use the library, and then it > > > would appear as 'feature, or I could alias 'feature to 'banana--you > > > get the idea. > > > > > > I don't want to reserve some magic symbol name that defies namespace > > > rules, so that if the library consumer code uses the symbol 'feature > > > to mean something different, they get bizarre results. > > > > > > What is a good pattern for writing the "matching" logic in such a > > > selectively-transforming macro so that it can properly find the > > > magic call it's looking for in the presence of normal namespacing > > > behavior? > > > > > > Thanks, > > > > > > -Kyle > > > > Hi, > > > > The following technique seems to work for finding out if you've > > > > been aliased: > > > > (ns somewhere.trial) > > > > (let [here *ns*] > > > > (defmacro whats-my-name [] > > > > (some (fn [[k v]] (when (= here v) `(quote ~k))) > > > > (ns-aliases *ns*)))) > > > > user> (require '[somewhere.trial :as aliased]) => > > user> (aliased/whats-my-name) => aliased > > > > So at the top of with-feature the parser could check for an alias and > > construct the appropriate predicate from the result. > > > > -Andy > > I originally had something similar to this actually, but it doesn't work > for the case when the library is referred in the consumer code with :use > because the symbol's namespace is then nil, and you still can't tell if > they're shadowing it with a let binding, or have renamed it with :as. > > However, this idea occurred to me yesterday. What if I check to see if > the symbol is pointing to the *var* containing my magic function, > instead of trying to examine the symbol itself? e.g.: > > (= (resolve symbol-i-am-scanning-in-my-macro) > #'function-i-am-looking-for) > > It seems to work, since at macro-expand time *ns* is bound to the > consumer code's namespace. Does this seem like a reasonable way to deal > with this? > > -Kyle -- 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
