diff --git a/docs/libraries.md b/docs/libraries.md
index 12f4ef9..7d42ab6 100644
--- a/docs/libraries.md
+++ b/docs/libraries.md
@@ -48,6 +48,10 @@ e.g. the [ring-app example](https://github.com/jolt-lang/examples/tree/main/ring
   [data.priority-map](https://github.com/clojure/data.priority-map).
 * [core.memoize](https://github.com/clojure/core.memoize) — function memoization
   over [core.cache](https://github.com/clojure/core.cache).
+* [core.async](https://github.com/clojure/core.async) — CSP channels and `go` blocks
+  (`<!`/`>!`/`alts!`, `pipeline`, `mult`/`mix`/`pub`/`sub`) on real OS threads.
+* [core.logic](https://github.com/clojure/core.logic) — relational logic programming
+  (unification, `run`/`fresh`/`conde`, finite domains).
 * [tick](https://github.com/juxt/tick) — date/time over Jolt's `java.time`;
   `#time/…` literals via `time-literals`.
 * [transit-jolt](https://github.com/jolt-lang/transit-jolt) — Transit (JSON) read/write
diff --git a/host/chez/java/async.ss b/host/chez/java/async.ss
index ee200a0..98a4a11 100644
--- a/host/chez/java/async.ss
+++ b/host/chez/java/async.ss
@@ -1,17 +1,20 @@
-;; async.ss — clojure.core.async on real OS threads for the Chez host.
+;; async.ss — clojure.core.async channel primitives on real OS threads.
 ;;
-;; A `go` block is an OS thread and a channel is a mutex+condition blocking
-;; queue: <! / >! are the blocking <!! / >!! (they "park" by blocking the thread).
-;; <! / >! work ANYWHERE — no CPS transform — because they are ordinary blocking
-;; calls. Real parallelism, shared heap. Trade-off: one OS thread per go block
-;; (fine for typical use, not for thousands of simultaneous go blocks).
+;; A `go` block is an OS thread and a channel is a Chez mutex+condition blocking
+;; queue: <! / >! are the blocking <!! / >!! (they "park" by blocking the thread),
+;; and work ANYWHERE — no CPS transform, no go-only restriction. Real parallelism,
+;; shared heap. This is a superset of the JVM model: it has no fixed go-block
+;; thread pool, no MAX-QUEUE-SIZE on pending ops, and parking ops are legal outside
+;; a go block. One OS thread per go block (fine for typical use).
 ;;
 ;; Channel: an unbuffered channel is a rendezvous (the putter blocks until its
 ;; value is taken); a buffered (chan n) put blocks only when full; dropping/sliding
-;; buffers never block the putter. A transducer is applied on the put side.
+;; buffers never block the putter. A transducer is applied on the put side; an
+;; optional ex-handler catches a throw from the transducer step.
 ;;
-;; The fns are def-var!'d into clojure.core.async; go/go-loop/thread are macros
-;; (mark-macro!) expanding to go-spawn. Loaded after
+;; This file provides the primitives; the higher-level dataflow API (mult, mix,
+;; pub/sub, pipeline, map, merge, reduce, …) is a Clojure overlay over them.
+;; go/go-loop/thread are macros (mark-macro!) expanding to go-spawn. Loaded after
 ;; concurrency.ss (reuses ms->duration). Requires a threaded Chez build.
 
 ;; --- buffers ----------------------------------------------------------------
@@ -19,6 +22,8 @@
 (define (jolt-async-buffer n)          (make-async-buffer n 'fixed))
 (define (jolt-async-dropping-buffer n) (make-async-buffer n 'dropping))
 (define (jolt-async-sliding-buffer n)  (make-async-buffer n 'sliding))
+(define (jolt-async-unblocking-buffer? b)
+  (if (and (async-buffer? b) (memq (async-buffer-kind b) '(dropping sliding promise))) #t #f))
 
 ;; --- channels ---------------------------------------------------------------
 ;; items: an amortized-O(1) FIFO held as a mutable #(out in len) — `out` is the
@@ -27,9 +32,12 @@
 ;; Each entry is (value . box); box is #f for a buffered value or a 1-slot vector
 ;; for an unbuffered rendezvous put (set #t when taken, waking the putter).
 ;; cap 0 + kind 'unbuffered = rendezvous; cap>0 with kind fixed/dropping/sliding.
+;; takew counts threads parked in a blocking take (so a non-blocking offer! to an
+;; unbuffered channel can tell a taker is waiting). xrf is the transducer reducing
+;; fn (or #f); exh the ex-handler (or #f).
 (define-record-type async-chan
-  (fields mu cv (mutable items) cap kind (mutable closed?) (mutable xrf))
-  (nongenerative async-chan-v1))
+  (fields mu cv (mutable items) cap kind (mutable closed?) (mutable xrf) (mutable takew) exh)
+  (nongenerative async-chan-v2))
 
 (define (ac-qnew) (vector '() '() 0))
 (define (ac-qlen ch) (vector-ref (async-chan-items ch) 2))
@@ -73,17 +81,30 @@
           ((null? (cdr args)) (car args))                     ; completion
           (else (ac-buf-give! ch (cadr args)) (car args)))))  ; step
 
-(define (ac-make cap kind xrf) (make-async-chan (make-mutex) (make-condition) (ac-qnew) cap kind #f xrf))
+;; run the transducer step (or completion) guarded by the channel's ex-handler:
+;; if the xform throws and exh returns non-nil, that value is added to the buffer.
+(define (ac-xrf-apply ch . v)
+  (let ((xrf (async-chan-xrf ch)) (exh (async-chan-exh ch)))
+    (guard (e (#t (if exh
+                      (let ((else (jolt-invoke exh e)))
+                        (unless (jolt-nil? else) (ac-buf-give! ch else))
+                        (async-chan-xrf ch))   ; treat as non-reduced
+                      (raise e))))
+      (apply jolt-invoke xrf ch v))))
 
-;; (chan) | (chan n) | (chan buf) | (chan n|buf xform)
+(define (ac-make cap kind xrf) (make-async-chan (make-mutex) (make-condition) (ac-qnew) cap kind #f xrf 0 #f))
+(define (ac-make/exh cap kind exh) (make-async-chan (make-mutex) (make-condition) (ac-qnew) cap kind #f #f 0 exh))
+
+;; (chan) | (chan n) | (chan buf) | (chan n|buf xform) | (chan n|buf xform exh)
 (define (jolt-async-chan . args)
   (let ((buf (if (pair? args) (car args) jolt-nil))
-        (xform (if (and (pair? args) (pair? (cdr args))) (cadr args) jolt-nil)))
+        (xform (if (and (pair? args) (pair? (cdr args))) (cadr args) jolt-nil))
+        (exh (if (and (pair? args) (pair? (cdr args)) (pair? (cddr args))) (caddr args) jolt-nil)))
     (let-values (((cap kind)
                   (cond ((async-buffer? buf) (values (async-buffer-n buf) (async-buffer-kind buf)))
                         ((and (number? buf) (> buf 0)) (values buf 'fixed))
                         (else (values 0 'unbuffered)))))
-      (let ((ch (ac-make cap kind #f)))
+      (let ((ch (ac-make/exh cap kind (if (jolt-nil? exh) #f exh))))
         (unless (jolt-nil? xform)
           (async-chan-xrf-set! ch (jolt-invoke xform (ac-make-add-rf ch))))
         ch))))
@@ -93,7 +114,7 @@
 (define (ac-close! ch)
   (unless (async-chan-closed? ch)
     (async-chan-closed?-set! ch #t)
-    (when (async-chan-xrf ch) (guard (e (#t #f)) (jolt-invoke (async-chan-xrf ch) ch)))
+    (when (async-chan-xrf ch) (guard (e (#t #f)) (ac-xrf-apply ch)))
     (condition-broadcast (async-chan-cv ch)))
   jolt-nil)
 (define (jolt-async-close! ch) (with-mutex (async-chan-mu ch) (ac-close! ch)))
@@ -102,12 +123,12 @@
 ;; transducer the value is run through it (one put -> zero or more channel values);
 ;; a `reduced` result closes the channel.
 (define (jolt-async-give ch v)
-  (when (jolt-nil? v) (jolt-throw (jolt-ex-info "Can't put nil on a channel" (jolt-hash-map))))
+  (when (jolt-nil? v) (jolt-throw (jolt-host-throwable "java.lang.IllegalArgumentException" "Can't put nil on a channel")))
   (with-mutex (async-chan-mu ch)
     (cond
       ((async-chan-closed? ch) #f)
       ((async-chan-xrf ch)
-       (let ((r (jolt-invoke (async-chan-xrf ch) ch v)))
+       (let ((r (ac-xrf-apply ch v)))
          (when (jolt-reduced? r) (ac-close! ch))
          #t))
       (else
@@ -154,12 +175,19 @@
       (cond ((eq? (async-chan-kind ch) 'promise)
              (cond ((not (ac-qempty? ch)) (ac-peek ch))
                    ((async-chan-closed? ch) jolt-nil)
-                   (else (condition-wait (async-chan-cv ch) (async-chan-mu ch)) (loop))))
+                   (else (ac-take-wait ch) (loop))))
             ((not (ac-qempty? ch)) (ac-take-head! ch))
             ((async-chan-closed? ch) jolt-nil)
-            (else (condition-wait (async-chan-cv ch) (async-chan-mu ch)) (loop))))))
+            (else (ac-take-wait ch) (loop))))))
 
-;; non-blocking take for alts!: a value, jolt-nil (closed+empty), or ac-poll-empty.
+;; park in a take, tracking the waiter count so a concurrent offer! to an
+;; unbuffered channel can see that a taker is ready.
+(define (ac-take-wait ch)
+  (async-chan-takew-set! ch (fx+ 1 (async-chan-takew ch)))
+  (condition-wait (async-chan-cv ch) (async-chan-mu ch))
+  (async-chan-takew-set! ch (fx- (async-chan-takew ch) 1)))
+
+;; non-blocking take for alts!/poll!: a value, jolt-nil (closed+empty), or ac-poll-empty.
 (define ac-poll-empty (list 'empty))
 (define (ac-poll! ch)
   (with-mutex (async-chan-mu ch)
@@ -168,28 +196,40 @@
           ((async-chan-closed? ch) jolt-nil)
           (else ac-poll-empty))))
 
-;; (alts! [ch ...]) — take from whichever channel is ready first; returns
-;; [value channel] (value nil if that channel closed). Take-only: every port must
-;; be a channel — put specs [ch val] and the :default option are not supported, so
-;; reject them with a clear error instead of crashing inside ac-poll!.
-;; Polls with a 1ms backoff — no cross-channel wait-set yet.
-(define ac-1ms (make-time 'time-duration 1000000 0))
-(define (jolt-async-alts chans)
-  (let ((cs (seq->list (jolt-seq chans))))
-    (for-each (lambda (c)
-                (unless (async-chan? c)
-                  (jolt-throw (jolt-ex-info
-                                "alts! supports channel ports only (put specs [ch val] and :default are not supported)"
-                                (jolt-hash-map)))))
-              cs)
-    (let loop ()
-      (let try ((rest cs))
-        (if (null? rest)
-            (begin (sleep ac-1ms) (loop))
-            (let ((r (ac-poll! (car rest))))
-              (if (eq? r ac-poll-empty)
-                  (try (cdr rest))
-                  (jolt-vector r (car rest)))))))))
+;; non-blocking give: 'ok (accepted), 'full (would block), or 'closed.
+(define (ac-try-give! ch v)
+  (when (jolt-nil? v) (jolt-throw (jolt-host-throwable "java.lang.IllegalArgumentException" "Can't put nil on a channel")))
+  (with-mutex (async-chan-mu ch)
+    (cond
+      ((async-chan-closed? ch) 'closed)
+      ((async-chan-xrf ch) (let ((r (ac-xrf-apply ch v)))
+                             (when (jolt-reduced? r) (ac-close! ch)) 'ok))
+      (else
+       (case (async-chan-kind ch)
+         ((dropping sliding) (ac-buf-give! ch v) 'ok)
+         ((promise) (when (ac-qempty? ch) (ac-qpush! ch (cons v #f))
+                          (condition-broadcast (async-chan-cv ch))) 'ok)
+         (else
+          (cond
+            ((> (async-chan-cap ch) 0)
+             (if (< (ac-qlen ch) (async-chan-cap ch))
+                 (begin (ac-qpush! ch (cons v #f)) (condition-broadcast (async-chan-cv ch)) 'ok)
+                 'full))
+            ;; unbuffered: only immediate if a taker is parked to receive it.
+            ((> (async-chan-takew ch) 0)
+             (let ((box (vector #f)))
+               (ac-qpush! ch (cons v box))
+               (condition-broadcast (async-chan-cv ch))
+               'ok))
+            (else 'full))))))))
+
+;; offer! / poll! — never block. offer! returns #t/#f(closed) on completion, nil if
+;; it would block; poll! returns a value, nil (closed+empty), or the ::none sentinel.
+(define cca-none (keyword "clojure.core.async" "none"))
+(define (jolt-async-offer! ch v)
+  (case (ac-try-give! ch v) ((ok) #t) ((closed) #f) (else jolt-nil)))
+(define (jolt-async-poll! ch)
+  (let ((r (ac-poll! ch))) (if (eq? r ac-poll-empty) cca-none r)))
 
 ;; (timeout ms) — a channel that closes after ms milliseconds.
 (define (jolt-async-timeout ms)
@@ -197,17 +237,28 @@
     (fork-thread (lambda () (sleep (ms->duration ms)) (jolt-async-close! w)))
     w))
 
-;; (put! ch v [cb]) / (take! ch cb) — async put/take on a thread, optional callback.
-(define (jolt-async-put! ch v . cb)
-  (fork-thread (lambda ()
-                 (let ((ok (jolt-async-give ch v)))
-                   (when (and (pair? cb) (not (jolt-nil? (car cb)))) (jolt-invoke (car cb) ok)))))
-  jolt-nil)
-(define (jolt-async-take! ch cb)
-  (fork-thread (lambda ()
-                 (let ((v (jolt-async-take ch)))
-                   (unless (jolt-nil? cb) (jolt-invoke cb v)))))
-  jolt-nil)
+;; (put! ch v [cb [on-caller?]]) — async put, optional completion callback. If the
+;; put completes immediately and on-caller? (default #t), the callback runs on the
+;; calling thread; otherwise on another thread. Returns true unless already closed.
+(define (jolt-async-put! ch v . rest)
+  (let* ((cb (if (pair? rest) (car rest) jolt-nil))
+         (on-caller? (if (and (pair? rest) (pair? (cdr rest))) (jolt-truthy? (cadr rest)) #t))
+         (call-cb (lambda (ok) (unless (jolt-nil? cb) (jolt-invoke cb ok)))))
+    (case (ac-try-give! ch v)
+      ((ok) (if on-caller? (call-cb #t) (fork-thread (lambda () (call-cb #t)))) #t)
+      ((closed) (if on-caller? (call-cb #f) (fork-thread (lambda () (call-cb #f)))) #f)
+      (else (fork-thread (lambda () (call-cb (jolt-async-give ch v)))) #t))))
+
+;; (take! ch cb [on-caller?]) — async take. Same on-caller? rule as put!.
+(define (jolt-async-take! ch cb . rest)
+  (let* ((on-caller? (if (pair? rest) (jolt-truthy? (car rest)) #t))
+         (call-cb (lambda (v) (unless (jolt-nil? cb) (jolt-invoke cb v))))
+         (r (ac-poll! ch)))
+    (cond
+      ((eq? r ac-poll-empty) (fork-thread (lambda () (call-cb (jolt-async-take ch)))))
+      (on-caller? (call-cb r))
+      (else (fork-thread (lambda () (call-cb r)))))
+    jolt-nil))
 
 ;; (go-spawn thunk) — run thunk on a thread; return a buffered(1) channel that
 ;; conveys its value once then closes (a nil result just closes). Dynamic bindings
@@ -246,14 +297,19 @@
 (cca-def! "buffer" jolt-async-buffer)
 (cca-def! "dropping-buffer" jolt-async-dropping-buffer)
 (cca-def! "sliding-buffer" jolt-async-sliding-buffer)
+(cca-def! "__promise-buffer" (lambda () (make-async-buffer 1 'promise)))
+(cca-def! "unblocking-buffer?" jolt-async-unblocking-buffer?)
 (cca-def! "close!" jolt-async-close!)
 (cca-def! "<!" jolt-async-take)   (cca-def! "<!!" jolt-async-take)
 (cca-def! ">!" jolt-async-give)   (cca-def! ">!!" jolt-async-give)
-(cca-def! "alts!" jolt-async-alts) (cca-def! "alts!!" jolt-async-alts)
 (cca-def! "timeout" jolt-async-timeout)
 (cca-def! "put!" jolt-async-put!)
 (cca-def! "take!" jolt-async-take!)
+(cca-def! "offer!" jolt-async-offer!)
 (cca-def! "go-spawn" async-go-spawn)
+;; non-blocking primitives the Clojure overlay's do-alts polls over.
+(cca-def! "__poll!" jolt-async-poll!)
+(cca-def! "__offer!" jolt-async-offer!)
 (cca-def! "go" cca-go-macro)           (mark-macro! "clojure.core.async" "go")
 (cca-def! "go-loop" cca-go-loop-macro) (mark-macro! "clojure.core.async" "go-loop")
 (cca-def! "thread" cca-thread-macro)   (mark-macro! "clojure.core.async" "thread")
diff --git a/host/chez/loader.ss b/host/chez/loader.ss
index b456642..87d9db7 100644
--- a/host/chez/loader.ss
+++ b/host/chez/loader.ss
@@ -141,6 +141,14 @@
 (vector-for-each (lambda (c) (hashtable-set! loaded-ns (var-cell-ns c) #t))
                  (hashtable-values var-table))
 
+;; clojure.core.async ships native channel primitives (async.ss) AND a Clojure
+;; overlay (stdlib/clojure/core/async.clj) with the higher-level dataflow API
+;; (alts!, pipe, mult, mix, pub/sub, map, merge, …). The primitives pre-seed the
+;; namespace above, which would make a `require` no-op and skip the overlay. Drop
+;; it from the loaded set so a require pulls the overlay from the source roots
+;; (like clojure.test); the primitives stay defined either way.
+(hashtable-delete! loaded-ns "clojure.core.async")
+
 ;; Does `name` already have vars in the var-table? A namespace baked into the
 ;; image after the snapshot above — an AOT'd app namespace in a `jolt build`
 ;; binary — exists in memory with no source file; a later `require` of it must
diff --git a/host/chez/ns.ss b/host/chez/ns.ss
index cad5286..f65315f 100644
--- a/host/chez/ns.ss
+++ b/host/chez/ns.ss
@@ -74,7 +74,8 @@
                      ;; :refer :all — bring in every public var (require :refer :all)
                      ((and (keyword? v) (string=? (keyword-t-name v) "all"))
                       (chez-register-refer-all! cns target))
-                     ((pvec? v)
+                     ;; :refer [a b] or :refer (a b) — both forms list names to bring in.
+                     ((or (pvec? v) (cseq? v) (empty-list-t? v))
                       (for-each (lambda (n)
                                   (when (symbol-t? n) (chez-register-refer! cns (symbol-t-name n) target)))
                                 (seq->list v))))))))
diff --git a/host/chez/seq.ss b/host/chez/seq.ss
index 98401ad..9f70e75 100644
--- a/host/chez/seq.ss
+++ b/host/chez/seq.ss
@@ -249,10 +249,13 @@
     (jolt-persistent! (reduce-seq (lambda (t x) (jolt-conj! t x)) (jolt-transient-new to) (jolt-seq from)))))
 
 (define (range-from n) (cseq-lazy n (lambda () (range-from (+ n 1)))))
+;; An empty range is () (jolt-empty-list), NOT nil — (range 0) and (range 5 5) are
+;; empty seqs in Clojure, so (= () (range 0)) holds. The same () terminates the
+;; lazy tail of a non-empty range (jolt-empty-list seqs back to nil, see jolt-take).
 (define (range-bounded n end step)
   (if (if (> step 0.0) (< n end) (> n end))
       (cseq-lazy n (lambda () (range-bounded (+ n step) end step)))
-      jolt-nil))
+      jolt-empty-list))
 ;; numeric tower: exact 0/1 defaults so (range 3) yields exact ints
 ;; (= JVM longs); flonum args still produce flonums (Scheme arithmetic preserves).
 (define jolt-range
diff --git a/stdlib/clojure/core/async.clj b/stdlib/clojure/core/async.clj
new file mode 100644
index 0000000..5965100
--- /dev/null
+++ b/stdlib/clojure/core/async.clj
@@ -0,0 +1,667 @@
+;; clojure.core.async — higher-level dataflow API over the channel primitives.
+;;
+;; The primitives (chan, <!, >!, <!!, >!!, close!, put!, take!, offer!, timeout,
+;; promise-chan, buffer/dropping-buffer/sliding-buffer, go/go-loop/thread, go-spawn)
+;; are provided natively (host/chez/java/async.ss) on real OS threads. This overlay
+;; adds the portable dataflow operators — alts!, pipe, pipeline, split, reduce,
+;; transduce, mult, mix, pub/sub, map, merge, and the deprecated map</map>/… —
+;; ported from clojure.core.async over those primitives. Because go blocks are real
+;; threads, parking ops are ordinary blocking ops and work anywhere; this is a
+;; superset of the JVM model (no fixed thread pool, no pending-op limit).
+
+(ns clojure.core.async
+  (:refer-clojure :exclude [reduce transduce into merge map take partition partition-by]))
+
+;; --- alts -------------------------------------------------------------------
+;; do-alts polls each port non-blockingly under its own channel lock; the first
+;; ready op wins. A take port is ready when a value (or closed nil) is available;
+;; a put spec [ch val] is ready when the value can be offered. Polls with a 1ms
+;; backoff (no cross-channel wait-set).
+
+(defn- alt-attempt [port]
+  (if (vector? port)
+    (let [ch (nth port 0) v (nth port 1)]
+      (assert (some? v) "Can't put nil on channel")
+      (let [r (clojure.core.async/__offer! ch v)]   ; true | false (closed) | nil (would block)
+        (when (some? r) [r ch])))
+    (let [r (clojure.core.async/__poll! port)]       ; value | nil (closed) | ::none
+      (when (not= r ::none) [r port]))))
+
+(defn do-alts
+  "Returns [val port] for the first ready op among ports. ports is a vector of
+  take ports and/or [channel val] put specs. opts may include :priority true
+  (try in order) and :default val (return [val :default] if none ready)."
+  [ports opts]
+  (assert (pos? (count ports)) "alts must have at least one channel operation")
+  (let [ports (vec ports)
+        n (count ports)
+        priority (:priority opts)
+        has-default (contains? opts :default)]
+    ;; Scan ports from a random start (sequential, wrapping) so a non-priority alts
+    ;; is fair without allocating a fresh shuffle every poll. With :priority the scan
+    ;; starts at 0 (declared order). Returns the first ready op.
+    (loop [first? true]
+      (let [start (if priority 0 (rand-int n))
+            hit (loop [k 0]
+                  (when (< k n)
+                    (let [j (+ start k) i (if (< j n) j (- j n))]
+                      (or (alt-attempt (nth ports i))
+                          (recur (inc k))))))]
+        (cond
+          hit hit
+          (and first? has-default) [(:default opts) :default]
+          :else (do (Thread/sleep 1) (recur false)))))))
+
+(defn alts!!
+  "Completes at most one of several channel operations. ports is a vector of take
+  ports and/or [channel val] put specs. Returns [val port]. Blocks until ready."
+  [ports & {:as opts}]
+  (do-alts ports opts))
+
+(defn alts!
+  "Like alts!!. In jolt a go block is a real thread, so parking and blocking alts
+  are the same operation."
+  [ports & {:as opts}]
+  (do-alts ports opts))
+
+(defn poll!
+  "Takes a val from port if possible immediately. Never blocks. Returns the value
+  or nil."
+  [port]
+  (let [r (clojure.core.async/__poll! port)]
+    (when (not= r ::none) r)))
+
+;; --- thread variants --------------------------------------------------------
+
+(defn thread-call
+  "Executes f in another thread, returning a channel that receives f's result then
+  closes."
+  ([f] (clojure.core.async/go-spawn f))
+  ([f _workload] (clojure.core.async/go-spawn f)))
+
+(defmacro io-thread
+  "Executes body in another thread, returning a channel that receives the result
+  then closes."
+  [& body]
+  `(thread-call (fn [] ~@body) :io))
+
+;; --- pipe / pipeline --------------------------------------------------------
+
+(defn pipe
+  "Takes elements from the from channel and supplies them to the to channel.
+  Closes to when from closes unless close? is false."
+  ([from to] (pipe from to true))
+  ([from to close?]
+   (go-loop []
+     (let [v (<! from)]
+       (if (nil? v)
+         (when close? (close! to))
+         (when (>! to v)
+           (recur)))))
+   to))
+
+(defn- pipeline*
+  [n to xf from close? ex-handler type]
+  (assert (pos? n))
+  (let [jobs (chan n)
+        results (chan n)
+        process (fn [job]
+                  (if (nil? job)
+                    (do (close! results) nil)
+                    (let [v (nth job 0) p (nth job 1)
+                          res (chan 1 xf ex-handler)]
+                      (>!! res v)
+                      (close! res)
+                      (put! p res)
+                      true)))
+        afn (fn [job]
+              (if (nil? job)
+                (do (close! results) nil)
+                (let [v (nth job 0) p (nth job 1)
+                      res (chan 1)]
+                  (xf v res)
+                  (put! p res)
+                  true)))]
+    (dotimes [_ n]
+      (case type
+        (:blocking :compute) (thread
+                               (loop []
+                                 (let [job (<!! jobs)]
+                                   (when (process job)
+                                     (recur)))))
+        :async (go-loop []
+                 (let [job (<! jobs)]
+                   (when (afn job)
+                     (recur))))))
+    (go-loop []
+      (let [v (<! from)]
+        (if (nil? v)
+          (close! jobs)
+          (let [p (chan 1)]
+            (>! jobs [v p])
+            (>! results p)
+            (recur)))))
+    (go-loop []
+      (let [p (<! results)]
+        (if (nil? p)
+          (when close? (close! to))
+          (let [res (<! p)]
+            (loop []
+              (let [v (<! res)]
+                (when (and (not (nil? v)) (>! to v))
+                  (recur))))
+            (recur)))))))
+
+(defn pipeline
+  "Takes elements from from, applies transducer xf with parallelism n, supplies to
+  to. Outputs are ordered relative to inputs."
+  ([n to xf from] (pipeline n to xf from true))
+  ([n to xf from close?] (pipeline n to xf from close? nil))
+  ([n to xf from close? ex-handler] (pipeline* n to xf from close? ex-handler :compute)))
+
+(defn pipeline-blocking
+  "Like pipeline, for blocking operations."
+  ([n to xf from] (pipeline-blocking n to xf from true))
+  ([n to xf from close?] (pipeline-blocking n to xf from close? nil))
+  ([n to xf from close? ex-handler] (pipeline* n to xf from close? ex-handler :blocking)))
+
+(defn pipeline-async
+  "Like pipeline, for async fns af of two args [input result-channel]."
+  ([n to af from] (pipeline-async n to af from true))
+  ([n to af from close?] (pipeline* n to af from close? nil :async)))
+
+(defn split
+  "Splits ch by predicate p into [true-chan false-chan]."
+  ([p ch] (split p ch nil nil))
+  ([p ch t-buf-or-n f-buf-or-n]
+   (let [tc (chan t-buf-or-n)
+         fc (chan f-buf-or-n)]
+     (go-loop []
+       (let [v (<! ch)]
+         (if (nil? v)
+           (do (close! tc) (close! fc))
+           (when (>! (if (p v) tc fc) v)
+             (recur)))))
+     [tc fc])))
+
+;; --- reduce / transduce / collection sinks ----------------------------------
+
+(defn reduce
+  "Returns a channel with the single result of reducing ch with f from init."
+  [f init ch]
+  (go-loop [ret init]
+    (let [v (<! ch)]
+      (if (nil? v)
+        ret
+        (let [ret' (f ret v)]
+          (if (reduced? ret')
+            @ret'
+            (recur ret')))))))
+
+(defn transduce
+  "async/reduces ch with the transformation (xform f), returning a channel with the
+  result."
+  [xform f init ch]
+  (let [f (xform f)]
+    (go
+      (let [ret (<! (reduce f init ch))]
+        (f ret)))))
+
+(defn- bounded-count [n coll]
+  (if (counted? coll)
+    (min n (count coll))
+    (loop [i 0 s (seq coll)]
+      (if (and s (< i n))
+        (recur (inc i) (next s))
+        i))))
+
+(defn onto-chan!
+  "Puts the contents of coll into ch, closing ch after unless close? is false.
+  Returns a channel that closes when done."
+  ([ch coll] (onto-chan! ch coll true))
+  ([ch coll close?]
+   (go-loop [vs (seq coll)]
+     (if (and vs (>! ch (first vs)))
+       (recur (next vs))
+       (when close?
+         (close! ch))))))
+
+(defn to-chan!
+  "Returns a channel containing the contents of coll, closing when exhausted."
+  [coll]
+  (let [c (bounded-count 100 coll)]
+    (if (pos? c)
+      (let [ch (chan c)]
+        (onto-chan! ch coll)
+        ch)
+      (let [ch (chan)]
+        (close! ch)
+        ch))))
+
+(defn onto-chan!!
+  "Like onto-chan! for use when accessing coll might block."
+  ([ch coll] (onto-chan!! ch coll true))
+  ([ch coll close?]
+   (thread
+     (loop [vs (seq coll)]
+       (if (and vs (>!! ch (first vs)))
+         (recur (next vs))
+         (when close?
+           (close! ch)))))))
+
+(defn to-chan!!
+  "Like to-chan! for use when accessing coll might block."
+  [coll]
+  (let [c (bounded-count 100 coll)]
+    (if (pos? c)
+      (let [ch (chan c)]
+        (onto-chan!! ch coll)
+        ch)
+      (let [ch (chan)]
+        (close! ch)
+        ch))))
+
+(defn onto-chan
+  "Deprecated - use onto-chan! or onto-chan!!"
+  ([ch coll] (onto-chan! ch coll true))
+  ([ch coll close?] (onto-chan! ch coll close?)))
+
+(defn to-chan
+  "Deprecated - use to-chan! or to-chan!!"
+  [coll]
+  (to-chan! coll))
+
+(defn into
+  "Returns a channel with the single collection result of conjoining items from ch
+  onto coll. ch must close first."
+  [coll ch]
+  (reduce conj coll ch))
+
+(defn take
+  "Returns a channel that returns at most n items from ch, then closes."
+  ([n ch] (take n ch nil))
+  ([n ch buf-or-n]
+   (let [out (chan buf-or-n)]
+     (go (loop [x 0]
+           (when (< x n)
+             (let [v (<! ch)]
+               (when (not (nil? v))
+                 (>! out v)
+                 (recur (inc x))))))
+         (close! out))
+     out)))
+
+;; --- mult / tap -------------------------------------------------------------
+
+(defprotocol Mux
+  (muxch* [_]))
+
+(defprotocol Mult
+  (tap* [m ch close?])
+  (untap* [m ch])
+  (untap-all* [m]))
+
+(defn mult
+  "Creates a mult of ch. Copies can be created with tap and removed with untap.
+  Each item is distributed to all taps synchronously."
+  [ch]
+  (let [cs (atom {})
+        m (reify
+            Mux
+            (muxch* [_] ch)
+            Mult
+            (tap* [_ ch close?] (swap! cs assoc ch close?) nil)
+            (untap* [_ ch] (swap! cs dissoc ch) nil)
+            (untap-all* [_] (reset! cs {}) nil))
+        dchan (chan 1)
+        dctr (atom nil)
+        done (fn [_] (when (zero? (swap! dctr dec))
+                       (put! dchan true)))]
+    (go-loop []
+      (let [val (<! ch)]
+        (if (nil? val)
+          (doseq [[c close?] @cs]
+            (when close? (close! c)))
+          (let [chs (keys @cs)]
+            (reset! dctr (count chs))
+            (doseq [c chs]
+              (when-not (put! c val done)
+                (untap* m c)))
+            (when (seq chs)
+              (<! dchan))
+            (recur)))))
+    m))
+
+(defn tap
+  "Copies the mult source onto ch. Closes ch when the source closes unless close?
+  is false."
+  ([mult ch] (tap mult ch true))
+  ([mult ch close?] (tap* mult ch close?) ch))
+
+(defn untap
+  "Disconnects ch from a mult."
+  [mult ch]
+  (untap* mult ch))
+
+(defn untap-all
+  "Disconnects all channels from a mult."
+  [mult]
+  (untap-all* mult))
+
+;; --- mix --------------------------------------------------------------------
+
+(defprotocol Mix
+  (admix* [m ch])
+  (unmix* [m ch])
+  (unmix-all* [m])
+  (toggle* [m state-map])
+  (solo-mode* [m mode]))
+
+(defn mix
+  "Creates a mix of input channels put onto out. Inputs are added with admix,
+  removed with unmix, and toggled (:mute/:pause/:solo) with toggle."
+  [out]
+  (let [cs (atom {})
+        solo-modes #{:mute :pause}
+        solo-mode (atom :mute)
+        change (chan (sliding-buffer 1))
+        changed #(put! change true)
+        pick (fn [attr chs]
+               (reduce-kv
+                (fn [ret c v]
+                  (if (attr v) (conj ret c) ret))
+                #{} chs))
+        calc-state (fn []
+                     (let [chs @cs
+                           mode @solo-mode
+                           solos (pick :solo chs)
+                           pauses (pick :pause chs)]
+                       {:solos solos
+                        :mutes (pick :mute chs)
+                        :reads (conj
+                                (if (and (= mode :pause) (seq solos))
+                                  (vec solos)
+                                  (vec (remove pauses (keys chs))))
+                                change)}))
+        m (reify
+            Mux
+            (muxch* [_] out)
+            Mix
+            (admix* [_ ch] (swap! cs assoc ch {}) (changed))
+            (unmix* [_ ch] (swap! cs dissoc ch) (changed))
+            (unmix-all* [_] (reset! cs {}) (changed))
+            (toggle* [_ state-map] (swap! cs (partial merge-with clojure.core/merge) state-map) (changed))
+            (solo-mode* [_ mode]
+              (assert (solo-modes mode) (str "mode must be one of: " solo-modes))
+              (reset! solo-mode mode)
+              (changed)))]
+    (go-loop [state (calc-state)]
+      (let [{:keys [solos mutes reads]} state
+            [v c] (alts! reads)]
+        (if (or (nil? v) (= c change))
+          (do (when (nil? v)
+                (swap! cs dissoc c))
+              (recur (calc-state)))
+          (if (or (solos c)
+                  (and (empty? solos) (not (mutes c))))
+            (when (>! out v)
+              (recur state))
+            (recur state)))))
+    m))
+
+(defn admix
+  "Adds ch as an input to the mix."
+  [mix ch]
+  (admix* mix ch))
+
+(defn unmix
+  "Removes ch as an input to the mix."
+  [mix ch]
+  (unmix* mix ch))
+
+(defn unmix-all
+  "Removes all inputs from the mix."
+  [mix]
+  (unmix-all* mix))
+
+(defn toggle
+  "Atomically sets the state of one or more channels in a mix."
+  [mix state-map]
+  (toggle* mix state-map))
+
+(defn solo-mode
+  "Sets the solo mode of the mix (:mute or :pause)."
+  [mix mode]
+  (solo-mode* mix mode))
+
+;; --- pub / sub --------------------------------------------------------------
+
+(defprotocol Pub
+  (sub* [p v ch close?])
+  (unsub* [p v ch])
+  (unsub-all* [p] [p v]))
+
+(defn pub
+  "Creates a pub of ch partitioned by topic-fn. Subscribe with sub."
+  ([ch topic-fn] (pub ch topic-fn (constantly nil)))
+  ([ch topic-fn buf-fn]
+   (let [mults (atom {})
+         ensure-mult (fn [topic]
+                       (or (get @mults topic)
+                           (get (swap! mults
+                                       #(if (% topic) % (assoc % topic (mult (chan (buf-fn topic))))))
+                                topic)))
+         p (reify
+             Mux
+             (muxch* [_] ch)
+             Pub
+             (sub* [_p topic ch close?]
+               (let [m (ensure-mult topic)]
+                 (tap m ch close?)))
+             (unsub* [_p topic ch]
+               (when-let [m (get @mults topic)]
+                 (untap m ch)))
+             (unsub-all* [_] (reset! mults {}))
+             (unsub-all* [_ topic] (swap! mults dissoc topic)))]
+     (go-loop []
+       (let [val (<! ch)]
+         (if (nil? val)
+           (doseq [m (vals @mults)]
+             (close! (muxch* m)))
+           (let [topic (topic-fn val)
+                 m (get @mults topic)]
+             (when m
+               (when-not (>! (muxch* m) val)
+                 (swap! mults dissoc topic)))
+             (recur)))))
+     p)))
+
+(defn sub
+  "Subscribes ch to a topic of pub p."
+  ([p topic ch] (sub p topic ch true))
+  ([p topic ch close?] (sub* p topic ch close?)))
+
+(defn unsub
+  "Unsubscribes ch from a topic of pub p."
+  [p topic ch]
+  (unsub* p topic ch))
+
+(defn unsub-all
+  "Unsubscribes all channels from a pub, or from a topic."
+  ([p] (unsub-all* p))
+  ([p topic] (unsub-all* p topic)))
+
+;; --- map / merge ------------------------------------------------------------
+
+(defn map
+  "Applies f to the set of first items from each source channel, then second, etc.
+  Closes the output channel when any source closes."
+  ([f chs] (map f chs nil))
+  ([f chs buf-or-n]
+   (let [chs (vec chs)
+         out (chan buf-or-n)
+         cnt (count chs)
+         rets (atom (vec (repeat cnt nil)))
+         dchan (chan 1)
+         dctr (atom nil)
+         done (mapv (fn [i]
+                      (fn [ret]
+                        (swap! rets assoc i ret)
+                        (when (zero? (swap! dctr dec))
+                          (put! dchan @rets))))
+                    (range cnt))]
+     (if (zero? cnt)
+       (close! out)
+       (go-loop []
+         (reset! dctr cnt)
+         (dotimes [i cnt]
+           (take! (nth chs i) (nth done i)))
+         (let [rets (<! dchan)]
+           (if (some nil? rets)
+             (close! out)
+             (do (>! out (apply f rets))
+                 (recur))))))
+     out)))
+
+(defn merge
+  "Returns a channel with all values taken from the source channels chs. Closes
+  after all sources close."
+  ([chs] (merge chs nil))
+  ([chs buf-or-n]
+   (let [out (chan buf-or-n)]
+     (go-loop [cs (vec chs)]
+       (if (pos? (count cs))
+         (let [[v c] (alts! cs)]
+           (if (nil? v)
+             (recur (filterv #(not= c %) cs))
+             (do (>! out v)
+                 (recur cs))))
+         (close! out)))
+     out)))
+
+;; --- deprecated channel ops (rewritten as go-loops) -------------------------
+
+(defn map<
+  "Deprecated - use a transducer. Returns a read-side channel mapping f over ch."
+  [f ch]
+  (let [out (chan)]
+    (go-loop []
+      (let [v (<! ch)]
+        (if (nil? v) (close! out) (do (>! out (f v)) (recur)))))
+    out))
+
+(defn map>
+  "Deprecated - use a transducer. Returns a write-side channel mapping f into out."
+  [f out]
+  (let [in (chan)]
+    (go-loop []
+      (let [v (<! in)]
+        (if (nil? v) (close! out) (do (>! out (f v)) (recur)))))
+    in))
+
+(defn filter<
+  "Deprecated - use a transducer."
+  ([p ch] (filter< p ch nil))
+  ([p ch buf-or-n]
+   (let [out (chan buf-or-n)]
+     (go-loop []
+       (let [val (<! ch)]
+         (if (nil? val)
+           (close! out)
+           (do (when (p val) (>! out val))
+               (recur)))))
+     out)))
+
+(defn remove<
+  "Deprecated - use a transducer."
+  ([p ch] (remove< p ch nil))
+  ([p ch buf-or-n] (filter< (complement p) ch buf-or-n)))
+
+(defn filter>
+  "Deprecated - use a transducer."
+  [p out]
+  (let [in (chan)]
+    (go-loop []
+      (let [v (<! in)]
+        (if (nil? v)
+          (close! out)
+          (do (when (p v) (>! out v))
+              (recur)))))
+    in))
+
+(defn remove>
+  "Deprecated - use a transducer."
+  [p out]
+  (filter> (complement p) out))
+
+(defn- mapcat* [f in out]
+  (go-loop []
+    (let [val (<! in)]
+      (if (nil? val)
+        (close! out)
+        (do (doseq [v (f val)]
+              (>! out v))
+            (recur))))))
+
+(defn mapcat<
+  "Deprecated - use a transducer."
+  ([f in] (mapcat< f in nil))
+  ([f in buf-or-n]
+   (let [out (chan buf-or-n)]
+     (mapcat* f in out)
+     out)))
+
+(defn mapcat>
+  "Deprecated - use a transducer."
+  ([f out] (mapcat> f out nil))
+  ([f out buf-or-n]
+   (let [in (chan buf-or-n)]
+     (mapcat* f in out)
+     in)))
+
+(defn unique
+  "Deprecated - use a transducer. Drops consecutive duplicates."
+  ([ch] (unique ch nil))
+  ([ch buf-or-n]
+   (let [out (chan buf-or-n)]
+     (go (loop [last nil]
+           (let [v (<! ch)]
+             (when (not (nil? v))
+               (if (= v last)
+                 (recur last)
+                 (do (>! out v)
+                     (recur v))))))
+         (close! out))
+     out)))
+
+(defn partition
+  "Deprecated - use a transducer. Partitions ch into vectors of n."
+  ([n ch] (partition n ch nil))
+  ([n ch buf-or-n]
+   (let [out (chan buf-or-n)]
+     (go-loop [arr [] idx 0]
+       (let [v (<! ch)]
+         (if (not (nil? v))
+           (let [arr (conj arr v) new-idx (inc idx)]
+             (if (< new-idx n)
+               (recur arr new-idx)
+               (do (>! out arr) (recur [] 0))))
+           (do (when (> idx 0) (>! out arr))
+               (close! out)))))
+     out)))
+
+(defn partition-by
+  "Deprecated - use a transducer. Partitions ch by runs of (f v)."
+  ([f ch] (partition-by f ch nil))
+  ([f ch buf-or-n]
+   (let [out (chan buf-or-n)]
+     (go-loop [lst [] last ::nothing]
+       (let [v (<! ch)]
+         (if (not (nil? v))
+           (let [new-itm (f v)]
+             (if (or (= new-itm last) (identical? last ::nothing))
+               (recur (conj lst v) new-itm)
+               (do (>! out lst) (recur [v] new-itm))))
+           (do (when (> (count lst) 0) (>! out lst))
+               (close! out)))))
+     out)))
diff --git a/stdlib/clojure/core/async/lab.clj b/stdlib/clojure/core/async/lab.clj
new file mode 100644
index 0000000..b8c8890
--- /dev/null
+++ b/stdlib/clojure/core/async/lab.clj
@@ -0,0 +1,34 @@
+;; clojure.core.async.lab — experimental features over the channel primitives.
+;;
+;; multiplex/broadcast are ported as go-loops over jolt's primitives (the JVM
+;; versions reify the impl handler protocol, which jolt does not expose).
+
+(ns clojure.core.async.lab
+  (:require [clojure.core.async :as async]))
+
+(defn multiplex
+  "Returns a read port that yields values from whichever of ports is ready. A
+  closed port is dropped; the multiplex port closes once all ports have closed."
+  [& ports]
+  (let [out (async/chan)]
+    (async/go-loop [cs (vec ports)]
+      (if (pos? (count cs))
+        (let [[v c] (async/alts! cs)]
+          (if (nil? v)
+            (recur (filterv #(not= c %) cs))
+            (do (async/>! out v)
+                (recur cs))))
+        (async/close! out)))
+    out))
+
+(defn broadcast
+  "Returns a write port that writes each value to all of ports. A write parks until
+  the value has been written to every port."
+  [& ports]
+  (let [in (async/chan)]
+    (async/go-loop []
+      (let [v (async/<! in)]
+        (when (some? v)
+          (doseq [p ports] (async/>! p v))
+          (recur))))
+    in))
diff --git a/test/chez/corpus.edn b/test/chez/corpus.edn
index 04f385b..93fa003 100644
--- a/test/chez/corpus.edn
+++ b/test/chez/corpus.edn
@@ -3349,4 +3349,8 @@
   {:suite "symbols / interning" :label "equal symbols share an interned name string" :expected "true" :actual "(let [a (quote ?foo) b (quote ?foo)] (identical? (name a) (name b)))"}
   {:suite "reader / unquote" :label "~x reads as clojure.core/unquote" :expected "true" :actual "(= (quote (clojure.core/unquote v)) (read-string \"~v\"))"}
   {:suite "reader / unquote" :label "~@x reads as clojure.core/unquote-splicing" :expected "true" :actual "(= (quote clojure.core/unquote-splicing) (first (read-string \"~@xs\")))"}
+  {:suite "clojure.core / range" :label "(range 0) is the empty seq ()" :expected "true" :actual "(= () (range 0))"}
+  {:suite "clojure.core / range" :label "(range 5 5) is the empty seq ()" :expected "true" :actual "(= () (range 5 5))"}
+  {:suite "clojure.core / range" :label "empty range is not nil" :expected "true" :actual "(some? (range 5 0))"}
+  {:suite "clojure.core / range" :label "empty range count" :expected "0" :actual "(count (range 0))"}
 ]