http://pedestal.io/pedestal/0.7-pre/guides/defining-routes.html says "The simplest route has just a URL, an HTTP verb, and a handler:

["/users" :get view-users]

A function is treated as a handler function, not an interceptor record.

If the value after the method (:get) is a vector, then it should be a vector of interceptors. Technically, things that satisfy the IntoInterceptor protocol.

(defprotocol IntoInterceptor
  (-interceptor [t] "Given a value, produce an Interceptor Record."))

(declare interceptor)
(extend-protocol IntoInterceptor

  IPersistentMap
  (-interceptor [t] (map->Interceptor t))

  ; This is the `handler` case
  Fn
  (-interceptor [t]
    (let [int-meta (meta t)]
      ;; To some degree, support backwards compatibility
      (if (or (:interceptor int-meta)
              (:interceptorfn int-meta))
        (interceptor (t))
        (interceptor {:enter (fn [context]
                               (assoc context :response (t (:request context))))}))))

  IPersistentList
  (-interceptor [t] (interceptor (eval t)))

  Cons
  (-interceptor [t] (interceptor (eval t)))

  Symbol
  (-interceptor [t] (interceptor (resolve t)))

  Var
  (-interceptor [t] (interceptor (deref t)))

  Interceptor
  (-interceptor [t] t))

So Maps get converted to Interceptor records.

Functions are normally handlers, though with (not documented but in this code!) metadata, they can be functions that returns interceptors. Symbols are resolved, and Vars are de-refed. This is all still pretty static though, as the resolving/deref-ing/invoking all happens at route expansion time, thus the need for all the tricks here: http://pedestal.io/pedestal/0.7-pre/guides/live-repl.html

I'm thinking of introducing some macros, keyed off of system properties or env vars, to make this more straight forward.

thank you very much 🙂