Hi,
I'm building a REST server library on top of compojure loosely modeled
after the ideas of erlangs webmachine. The idea is to describe a
resource using a couple of function which server as decision makers
for the different stages of HTTP request processing. There will be a
function to determine if the request method is allowed, if the request
is authorized, a method to produce an ETAG or to process the request
body in case of a POST request. Something like
(defn valid-method? [request] (= (get-method request) :get)
(defn generate-etag [request] (make-hash-md5 (get-path request)))
(defn process-post [request] (str "The body was" (get-body request))
The question is: how can on group the methods together for different
resources and to enable fall back do default implementation of the
methods (e.g. generate an etag by sha-ing the response body)?
Two solutions come to my mind: multimethods and maps of methods.
For multimethods id declare a type :rest-ressource which methods will
serve as a default implementation and that could be overridden by each
sub type resource.
By maps of methods I mean something like
(def rest-default-impl {
:valid-method? (fn [request] (contains [:head :get] (get-method
request)))
# ...
})
(defn make-rest [method-map]
(merge rest-default-impl method-map))
(def test-resource make-rest({ :valid-method? (fn [request] (= (get-
method request) :get))
:body { :text/html (fn
[request] "Hello, world.") }}))
Which way would you prefer? What are to advantaces and drawbacks of
each? The method-map approach seams more fp to me, but, I think that's
like how multimethods are impemented, aren't they?
-billy.
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