blah.clj

(defmacro state->
  "[macro] Threads state through functions
   args: [init & clauses]
     init is the initial state value
     clauses look like -> clauses, either functions or lists.
     like ->, we insert the state into the second position
   returns: [final-state returns]
     returns is a vector of the return values in order of threading"
  [init & clauses]
  (if (seq clauses)
    (let [sym `state#
          form (fn [f]
                 (cond (list? f) `(~(first f) ~sym ~@(rest f))
                       (fny? f)  (list f sym)
                       :else (throw (ex-info (str "Don't know what to do with " f) {:got f}))))
          ns (repeatedly (count clauses) #(gensym "r"))
          binds (map (fn [r] [sym r]) ns)
          forms (map form clauses)
          lets (interleave binds forms)]
      (prn :sym sym :init init :lets lets :ns ns)
      `(let [~sym init ~@lets]
         [~sym [~@ns]]))
    init))

(macroexpand-1 '(state-> 123 :a (:b 456) (:c 7 8 9) :d))
;; =>

(clojure.core/let [state__15418__auto__ postgrey.squirrel.util/init
                   [state__15418__auto__ r15432] (:a state__15418__auto__)
                   [state__15418__auto__ r15433] (:b state__15418__auto__ 456)
                   [state__15418__auto__ r15434] (:c state__15418__auto__ 7 8 9)
                   [state__15418__auto__ r15435] (:d state__15418__auto__)]
  [state__15418__auto__ [r15432 r15433 r15434 r15435]])