Here's how plugin support is implemented in Waterfront:
The last expression in each plugin is the "plguin init function": a
function (can be anonymous) that takes a single parameter (a map) and
returns new map.
The load-plugin function takes a strings (specifying the path to
a .clj file), and performs load-file on each string. Then, load-plugin
evals the value returned by load-file (which, in fact, is the plugin
init function) passing a map as a parameter. If you're loading several
plugins the result returned from the init function will be used as the
new map passed to the next plugin.
Anyway, enough talking, let's go coding:
; say myutil/ut1.clj contains
(ns 'myutil.ut1)
(defn foo [] :foo-ut1)
; init function of ut1
(fn [m] (assoc m :foo foo))
; and myutil/ut2.clj contains
(ns 'myutil.ut2)
(defn foo [] :foo-ut2)
; init function of ut2
(fn [m] (assoc m :foo foo))
(defn load-plugin [path]
((load-file path) {}) )
;mylib/lib1.clj
(defn libfoo []
(((load-plugin (if some-condition "myutil/ut1.clj" "myutil/
ut2.clj")) :foo)) )
That's it. In Waterfront this design is integrated with the context
pattern which I described here a few days ago.
Hope that helps.
--
Itay Maman
http://javadots.blogspot.com
On Mar 5, 6:48 am, Adrian Cuthbertson <adrian.cuthbert...@gmail.com>
wrote:
> Hi,
>
> How would one create a "plugin" modular composition using clojure
> functions/modules only (i.e without resorting to java interface/
> plugin class implementations)?
>
> For example;
> ; say myutil/ut1.clj contains
> (ns 'myutil.ut1)
> (defn foo [] :foo-ut1)
>
> ; and myutil/ut2.clj contains
> (ns 'myutil.ut2)
> (defn foo [] :foo-ut2)
>
> ;and mylib/lib1.clj contains
> (defn libfoo [] (foo))
>
> Then from my app, I'd like to tell mylib.lib1 which ut to use when it
> loads, before calling libfoo.
> Is this possible, or is there some other clojure way of doing this?
>
> Thanks,
> Adrian.
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