fpcombinator

;; Non recursive function
(defn fib-nr [f]
  (fn [n]
    (if (< n 2) 1
        (+ ((f f) (- n 1))
           ((f f) (- n 2))))))
           
;; A U combinator that allows a generic application function 
(defn UM [myapply f]
  (defn g [v]
    (fn [args]
      (myapply (f v) args)))
  (f g))

;; Memoizer that is generic
(defn make-memoizer []
  (let [application-cache (atom {})]
    (fn [function args]
      (do
        (prn "ac" application-cache)
        (prn "args" args)
        (prn "fn" function)
        (if-let [e (find @application-cache args)]
          (val e)
          (let [result (apply function args)]
            (swap! application-cache assoc args result)
            result))))))

 ((UM (make-memoizer) fib-nr) 35); doesn't work - why?
 
 
 ((UM (make-memoizer) fib-nr) 1) ; works


;; Stack trace from the (.. 35) line
java.lang.IllegalArgumentException: Don't know how to create ISeq from: java.lang.Long
 at clojure.lang.RT.seqFrom (RT.java:505)
    clojure.lang.RT.seq (RT.java:486)
    clojure.core$seq.invoke (core.clj:133)
    clojure.core$apply.invoke (core.clj:624)
    viksit.explorations$make_memoizer$fn__13555.invoke (form-init7838994634444008614.clj:10)
    viksit.explorations$UM$g__13199$fn__13200.invoke (form-init7838994634444008614.clj:4)
    viksit.explorations$fib_nr$fn__11066.invoke (form-init7838994634444008614.clj:4)
    viksit.explorations$eval13956.invoke (form-init7838994634444008614.clj:1)
    clojure.lang.Compiler.eval (Compiler.java:6703)
    clojure.lang.Compiler.eval (Compiler.java:6666)
    clojure.core$eval.invoke (core.clj:2927)
    clojure.main$repl$read_eval_print__6625$fn__6628.invoke (main.clj:239)
    clojure.main$repl$read_eval_print__6625.invoke (main.clj:239)
    clojure.main$repl$fn__6634.invoke (main.clj:257)
    clojure.main$repl.doInvoke (main.clj:257)
    clojure.lang.RestFn.invoke (RestFn.java:1096)
    clojure.tools.nrepl.middleware.interruptible_eval$evaluate$fn__591.invoke (interruptible_eval.clj:56)
    clojure.lang.AFn.applyToHelper (AFn.java:152)
    clojure.lang.AFn.applyTo (AFn.java:144)
    clojure.core$apply.invoke (core.clj:624)
    clojure.core$with_bindings_STAR_.doInvoke (core.clj:1862)
    clojure.lang.RestFn.invoke (RestFn.java:425)
    clojure.tools.nrepl.middleware.interruptible_eval$evaluate.invoke (interruptible_eval.clj:41)
    clojure.tools.nrepl.middleware.interruptible_eval$interruptible_eval$fn__632$fn__635.invoke (interruptible_eval.clj:171)
    clojure.core$comp$fn__4192.invoke (core.clj:2402)
    clojure.tools.nrepl.middleware.interruptible_eval$run_next$fn__625.invoke (interruptible_eval.clj:138)
    clojure.lang.AFn.run (AFn.java:22)
    java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1145)
    java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:615)
    java.lang.Thread.run (Thread.java:744)

Finally, this can be fixed by using [function & args] in make-memoizer.