GraalVM polyglot interop between Clojure and JavaScript https://blog.taylorwood.io/2018/11/26/graal-polyglot.html

core.clj

(ns polydact.core
  (:import (clojure.lang IFn)
           (org.graalvm.polyglot Context Value)
           (org.graalvm.polyglot.proxy ProxyArray ProxyExecutable ProxyObject)))

(set! *warn-on-reflection* true)

(comment
  (do
    (def context
      (-> (Context/newBuilder (into-array ["js"]))
          (.allowHostAccess HostAccess/ALL)
          (.build)))

    (defn ^Value eval-js [code]
      (.eval ^Context context "js" code)))

  (.as (eval-js "Number.MAX_VALUE") Object)
  ;=> 1.7976931348623157E308
  (type *1)
  ;=> java.lang.Double

  (.as (eval-js "[{}]") Object)
  ;=> {"0" {}}
  (.as (eval-js "[{}]") java.util.List)
  ;=> ({})

  #_cool!)

(defn- execute
  [^Value execable & args]
  (.execute execable (object-array args)))

(declare value->clj)

(defmacro ^:private reify-ifn
  "Convenience macro for reifying IFn for executable polyglot Values."
  [v]
  (let [invoke-arity
        (fn [n]
          (let [args (map #(symbol (str "arg" (inc %))) (range n))]
            (if (seq args)
              ;; TODO test edge case for final `invoke` arity w/varargs
              `(~'invoke [this# ~@args] (value->clj (execute ~v ~@args)))
              `(~'invoke [this#] (value->clj (execute ~v))))))]
    `(reify IFn
       ~@(map invoke-arity (range 22))
       (~'applyTo [this# args#] (value->clj (apply execute ~v args#))))))
(macroexpand '(reify-ifn v))

(defn proxy-fn
  "Returns a ProxyExecutable instance for given function, allowing it to be
   invoked from polyglot contexts."
  [f]
  (reify ProxyExecutable
    (execute [_this args]
      (apply f (map value->clj args)))))

(defn value->clj
  "Returns a Clojure (or Java) value for given polyglot Value if possible,
   otherwise throws."
  [^Value v]
  (cond
    (.isNull v) nil
    (.isHostObject v) (.asHostObject v)
    (.isBoolean v) (.asBoolean v)
    (.isString v) (.asString v)
    (.isNumber v) (.as v Number)
    (.canExecute v) (reify-ifn v)
    (.hasArrayElements v) (into []
                                (for [i (range (.getArraySize v))]
                                  (value->clj (.getArrayElement v i))))
    (.hasMembers v) (into {}
                          (for [k (.getMemberKeys v)]
                            [k (value->clj (.getMember v k))]))
    :else (throw (Exception. "Unsupported value"))))

(comment
  (def js->clj (comp value->clj eval-js))

  (js->clj "[{}]")
  ;=> [{}]

  (js->clj "false")
  ;=> false
  (js->clj "3 / 3.33")
  ;=> 0.9009009009009009
  (js->clj "123123123123123123123123123123123")
  ;=> 1.2312312312312312E32

  (def doubler (js->clj "(n) => {return n * 2;}"))
  (doubler 2)
  ;=> 4

  (js->clj "m = {foo: 1, bar: '2', baz: {0: false}};")
  ;=> {"foo" 1, "bar" "2", "baz" {"0" false}}

  (def factorial
    (eval-js "
      var m = [];
      function factorial (n) {
        if (n == 0 || n == 1) return 1;
        if (m[n] > 0) return m[n];
        return m[n] = factorial(n - 1) * n;
      }
      x = {fn: factorial, memos: m};"))
  ((get (value->clj factorial) "fn") 12)
  ;=> 479001600
  (get (value->clj factorial) "memos")
  ;=> [nil nil 2 6 24 120 720 5040 40320 362880 3628800 39916800 479001600]
  ((get (value->clj factorial) "fn") 24)
  ;=> 6.204484017332394E23
  (get (value->clj factorial) "memos")
  ;=> [nil nil 2 6 24 120 720 5040 40320 362880 3628800 39916800 479001600 ... truncated for brevity]

  (eval-js "var foo = 0xFFFF")
  (eval-js "console.log(foo);")
  ;=> #object[org.graalvm.polyglot.Value 0x3f9d2028 "undefined"]
  ;65535

  (js->clj "1 + '1'")
  ;=> "11"
  (js->clj "['foo', 10, 2].sort()")
  ;=> [10 2 "foo"]

  (def js-aset
    (js->clj "(arr, idx, val) => { arr[idx] = val; return arr; }"))
  (js-aset (ProxyArray/fromArray (object-array [1 2 3])) 1 nil)
  ;=> [1 nil 3]

  (sort [{:b nil} \a 1 "a" "A" #{\a} :foo  -1 0 {:a nil} "bar"])
  (def js-sort
    (js->clj "(...vs) => { return vs.sort(); }"))
  (apply js-sort [{:b nil} \a 1 "a" "A" #{\a} :foo  -1 0 {:a nil} "bar"])
  ;=> [-1 0 1 "A" #{\a} :foo {:a nil} {:b nil} "a" "a" "bar"]

  (def variadic-fn
    (js->clj "(x, y, ...z) => { return [x, y, z]; }"))
  (apply variadic-fn :foo :bar (range 3))
  ;=> [:foo :bar [0 1 2]]

  (def ->json
    (js->clj "(x) => { return JSON.stringify(x); }"))
  (->json [1 2 3])
  ;=> "[1,2,3]"
  (->json (ProxyObject/fromMap {"foo" 1, "bar" nil}))
  ;=> "{\"foo\":1,\"bar\":null}"
  (def json->
    (js->clj "(x) => { return JSON.parse(x); }"))
  (json-> (->json [1 2 3]))
  ;=> [1 2 3]
  (json-> (->json (ProxyObject/fromMap {"foo" 1})))
  ;=> {"foo" 1}

  (def json-object
    (js->clj "(m) => { return m.foo + m.foo; }"))
  (json-object (ProxyObject/fromMap {"foo" 1}))
  ;=> 2

  (def clj-lambda
    (js->clj "
    m = {foo: [1, 2, 3],
         bar: {
           baz: ['a', 'z']
         }};
    (fn) => { return fn(m); }
    "))
  (clj-lambda
   (proxy-fn #(clojure.walk/prewalk
               (fn [v] (if (and (vector? v)
                                (not (map-entry? v)))
                         (vec (reverse v))
                         v))
               %)))
  ;=> {"foo" [3 2 1], "bar" {"baz" ["z" "a"]}}

  (def js-reduce
    (let [reduce (js->clj "(f, coll) => { return coll.reduce(f); }")
          reduce-init (js->clj "(f, coll, init) => { return coll.reduce(f, init); }")]
      (fn
        ([f coll] (reduce f coll))
        ([f init coll] (reduce-init f coll init)))))
  (js-reduce + (range 10))
  ;=> 45
  (js-reduce + -5.5 (range 10))
  ;=> 39.5
  (js-reduce (fn [acc elem]
               (assoc acc (keyword (str elem)) (doubler elem)))
             {}
             (range 5))
  ;=> {:0 0, :1 2, :2 4, :3 6, :4 8}

  (def log-coll
    (js->clj "(coll) => { for (i in coll) console.log(coll[i]); }"))
  (log-coll (repeatedly 3 #(do (prn 'sleeping)
                               (Thread/sleep 100)
                               (rand))))

  (log-coll (range))

  "nice")

Hey @taylorwood

Thanks for sharing this. I was trying it out and I was getting this error on the js-reduce method:

Execution error (PolyglotException) at <js>/:=> (Unnamed:1).
TypeError: invokeMember (reduce) on JavaObject[(0 1 2 3 4 5 6 7 8 9) (clojure.lang.LongRange)] failed due to: Unknown identifier: reduce

Any help I could get from you?
I'm running Java 8 & GraalVM 20

@kolharsam I think some Graal security stuff has changed since I wrote this. Try setting (.allowHostAccess context HostAccess/ALL). This works for me now:

(js-reduce + (range 10))
=> 45

More info here https://github.com/graalvm/graaljs/blob/master/docs/user/ScriptEngine.md. Thanks!

@taylorwood, thanks for helping out! It works for me too now.

I just had a few more questions if you don't mind:

1. (.as (eval-js "[{}]") Object) => I get the output for this as {} - any possible explanations?
2. I want to play around with this a little more. Could you point me to something interesting?
3. I also want to learn more about GraalVM any place that offers the best info apart from the docs?

Thanks again, @taylorwood

Hello @taylorwood,
I have found your interesting post on GraalVM Polyglot with Clojure and tried to play with it! Unfortunately when I try to run it with lein I have the following error
Exception in thread "main" java.lang.IllegalArgumentException: Could not find option with name version., compiling:(core.clj:30:14)
which refers to this line:
(def context (.build (Context/newBuilder (into-array ["js"]))))

No idea what I am doing wrong ! I am using GraalVM 20.1, java11 on Linux... The problem arise with dependency Clojure 1.9.0 or 1.10.1...
Thanks for any advice

@taylorwood very informative, thank you!