core.async + go block + map

simple_example.clj

(ns async-example.core
  (:require [clojure.core.async :refer :all])
  (:gen-class))

(defn -main [& args]
  (let [c (chan)]
    (go (>! c 1))
    (<!!
      (go
        (map <! [c])))))

stack_trace

$ lein run
Exception in thread "main" (java.lang.AssertionError: Assert failed: <! used not in (go ...) block
nil
        at clojure.core.async$_LT__BANG_.invoke(async.clj:81)
        at async_example.core$_main$fn__1378$state_machine__1165__auto____1379$fn__1382.invoke(core.clj:10)
        at clojure.core$map$fn__4207.invoke(core.clj:2485)
        at clojure.lang.LazySeq.sval(LazySeq.java:42)
        at clojure.lang.LazySeq.seq(LazySeq.java:60)
        at clojure.lang.RT.seq(RT.java:484)
        at clojure.core$seq.invoke(core.clj:133)
        at clojure.core$print_sequential.invoke(core_print.clj:46)
        at clojure.core$fn__5406.invoke(core_print.clj:143)
        at clojure.lang.MultiFn.invoke(MultiFn.java:231)
        at clojure.core$pr_on.invoke(core.clj:3322)
        at clojure.core$pr.invoke(core.clj:3334)
        at clojure.lang.AFn.applyToHelper(AFn.java:161)
        at clojure.lang.RestFn.applyTo(RestFn.java:132)
        at clojure.core$apply.invoke(core.clj:617)
        at clojure.core$prn.doInvoke(core.clj:3367)
        at clojure.lang.RestFn.invoke(RestFn.java:408)
        at clojure.main$eval_opt.invoke(main.clj:310)
        at clojure.main$initialize.invoke(main.clj:327)
        at clojure.main$null_opt.invoke(main.clj:362)
        at clojure.main$main.doInvoke(main.clj:440)
        at clojure.lang.RestFn.invoke(RestFn.java:421)
        at clojure.lang.Var.invoke(Var.java:419)
        at clojure.lang.AFn.applyToHelper(AFn.java:163)
        at clojure.lang.Var.applyTo(Var.java:532)
        at clojure.main.main(main.java:37)