(def-phase-fn cake-phase [x y] (+ x) (+ y))
pallet.extensions> (cake-phase 3 1 2)

;;Invalid session map in phase.
;;session is 4
;;Problem probably caused by subphase:
;;  (+ x)
;;Check for non crate functions, improper crate functions, or
;;      problems in threading the session map in your phase
;;      definition. A crate function is a function that takes a session
;;      map and other arguments, and returns a modified session
;;      map. Calls to crate functions are often wrapped in a threading
;;      macro, -> or pallet.phase/phase-fn, to simplify chaining of the
;;      session map argument.
;;  [Thrown class clojure.contrib.condition.Condition]