On Aug 31, 2008, at 4:34 AM, Frantisek Sodomka wrote:
> To extend this idea little further, lets define "code sections":
I like the idea a lot. I believe the "Aspect oriented programming"
folks call these kinds of "outside the main flow" items "aspects". I
think it would be good to have aspects defined in each namespace
rather than globally. (One might also argue for "in addition to"
globally.)
Here's an "aspects.clj" that resolves '+aspects+ at "compile time" in
the namespace where the function that uses it is defined:
(ns aspects)
(defmacro aspect [tag & body]
(when-let aspects# (ns-resolve *ns* '+aspects+)
(when (aspects# tag)
(cons 'do body))))
And a test:
(ns aspects.test
(:use aspects))
(def +aspects+ #{:debug :log0 :log1})
(defn myfn [x]
(aspect :debug
(printf "debugging info... (x = %s)\n" x))
(aspect :log0
(println "logging info..."))
(aspect :log1
(println "detailed logging info..."))
(* 2 x))
(myfn 10)
And a run:
user=> (require 'aspects.test :reload-all)
debugging info... (x = 10)
logging info...
detailed logging info...
nil
user=>
The code is written such that if +aspects+ is not defined in a
namespace, calls to "aspect" in that namespace generate no code. One
cool thing this leverages in Clojure is that +aspects+ can be either a
set (as shown) or a map from keyword to (generalized) boolean.
> Latest addition for libs to boot.clj also has this pattern, when
> using *loading-verbosely* flag.
That's a little different in that *loading-verbosely* is intended to
be dynamically bound at runtime rather than baked in at compile time.
I recall Rich suggesting recently that he prefers to see the * prefix
and suffix on symbols that are intended to be dynamically bound. Here
I'm suggesting that a + prefix and suffix be used for compile-time
constants. I've seen precedent for in Common Lisp.
> Any comments welcome, Frantisek
I think this is a fine idea that deserves some more discussion and
would make a good addition to clojure-contrib. Are you signed up to
contribute there yet?
--Steve
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