Can we support a subset of proxy?

[borkdude]

Goal: support a subset of proxy, e.g. proxy on APersistentMap like described in this blog post:

https://blog.wsscode.com/guide-to-custom-map-types/

/cc @GreshamDanielStephens @wilkerlucio

[borkdude]

A POC:

(defn proxy-fn [abstract-class methods]
  (case (.getName abstract-class)
    "clojure.lang.APersistentMap"
    (proxy
        [clojure.lang.APersistentMap]
        []
      (seq [] ((get methods 'seq)))
      (valAt ([k] ((get methods 'valAt) k))
        ([k d] ((get methods 'valAt) k d))))))

(def m (proxy-fn clojure.lang.APersistentMap
                 {'seq (fn []
                         (seq {:a 1 :b 2}))
                  'valAt (fn
                           ([k] k)
                           ([_k d] d))
                  'invoke (fn
                            ([k] k))}))

(prn (seq m)) ;; ([:a 1] [:b 2])
(prn (instance? clojure.lang.ILookup m)) ;; true
(prn (get m 1)) 1
(prn (instance? clojure.lang.IFn m)) ;; true
(prn (m 1)) ;; 1

[borkdude]

See https://github.com/babashka/babashka/blob/5555ea4ede9b7be3f2ab2ef7105264ec62bef680/test/babashka/proxy_test.clj

This is the code to support it from the babashka side:
https://github.com/babashka/babashka/blob/master/src/babashka/impl/proxy.clj

May need review