diff --git a/src/babashka/impl/clojure/data.clj b/src/babashka/impl/clojure/data.clj
index b15ba3ab..3d2a6fd7 100644
--- a/src/babashka/impl/clojure/data.clj
+++ b/src/babashka/impl/clojure/data.clj
@@ -1,10 +1,144 @@
-(ns babashka.impl.clojure.data
-  {:no-doc true}
-  (:require [clojure.data :as data]
-            [sci.impl.namespaces :refer [copy-var]]
-            [sci.impl.vars :as vars]))
+;   Copyright (c) Rich Hickey. All rights reserved.
+;   The use and distribution terms for this software are covered by the
+;   Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
+;   which can be found in the file epl-v10.html at the root of this distribution.
+;   By using this software in any fashion, you are agreeing to be bound by
+;   the terms of this license.
+;   You must not remove this notice, or any other, from this software.
 
-(def data-ns (vars/->SciNamespace 'clojure.data nil))
+(ns 
+  ^{:author "Stuart Halloway",
+    :doc "Non-core data functions."}
+  babashka.impl.clojure.data
+  (:require [clojure.set :as set]))
 
-(def data-namespace
-  {'diff       (copy-var data/diff data-ns)})
+(set! *warn-on-reflection* true)
+
+(declare diff)
+
+(defn- atom-diff
+  "Internal helper for diff."
+  [a b]
+  (if (= a b) [nil nil a] [a b nil]))
+
+;; for big things a sparse vector class would be better
+(defn- vectorize
+  "Convert an associative-by-numeric-index collection into
+   an equivalent vector, with nil for any missing keys"
+  [m]
+  (when (seq m)
+    (reduce
+     (fn [result [k v]] (assoc result k v))
+     (vec (repeat (apply max (keys m))  nil))
+     m)))
+
+(defn- diff-associative-key
+  "Diff associative things a and b, comparing only the key k."
+  [a b k]
+  (let [va (get a k)
+        vb (get b k)
+        [a* b* ab] (diff va vb)
+        in-a (contains? a k)
+        in-b (contains? b k)
+        same (and in-a in-b
+                  (or (not (nil? ab))
+                      (and (nil? va) (nil? vb))))]
+    [(when (and in-a (or (not (nil? a*)) (not same))) {k a*})
+     (when (and in-b (or (not (nil? b*)) (not same))) {k b*})
+     (when same {k ab})
+     ]))
+
+(defn- diff-associative
+  "Diff associative things a and b, comparing only keys in ks."
+  [a b ks]
+  (reduce
+   (fn [diff1 diff2]
+     (doall (map merge diff1 diff2)))
+   [nil nil nil]
+   (map
+    (partial diff-associative-key a b)
+    ks)))
+
+(defn- diff-sequential
+  [a b]
+  (vec (map vectorize (diff-associative
+                       (if (vector? a) a (vec a))
+                       (if (vector? b) b (vec b))
+                       (range (max (count a) (count b)))))))
+
+(defprotocol ^{:added "1.3"} EqualityPartition
+  "Implementation detail. Subject to change."
+  (^{:added "1.3"} equality-partition [x] "Implementation detail. Subject to change."))
+
+(defprotocol ^{:added "1.3"} Diff
+  "Implementation detail. Subject to change."
+  (^{:added "1.3"} diff-similar [a b] "Implementation detail. Subject to change."))
+
+(extend nil
+        Diff
+        {:diff-similar atom-diff})
+
+(extend Object
+        Diff
+        {:diff-similar (fn [^Object a ^Object b]
+                         ((if (.. a getClass isArray) diff-sequential atom-diff) a b))}
+        EqualityPartition
+        {:equality-partition
+         (fn [^Object x]
+           (if (.. x getClass isArray) :sequential :atom))})
+
+(extend-protocol EqualityPartition
+  nil
+  (equality-partition [x] :atom)
+  
+  java.util.Set
+  (equality-partition [x] :set)
+
+  java.util.List
+  (equality-partition [x] :sequential)
+  
+  java.util.Map
+  (equality-partition [x] :map))
+
+(defn- as-set-value
+  [s]
+  (if (set? s) s (into #{} s)))
+
+(extend-protocol Diff
+  java.util.Set
+  (diff-similar
+   [a b]
+   (let [aval (as-set-value a)
+         bval (as-set-value b)]
+     [(not-empty (set/difference aval bval))
+      (not-empty (set/difference bval aval))
+      (not-empty (set/intersection aval bval))]))
+  
+  java.util.List
+  (diff-similar [a b]
+    (diff-sequential a b))
+  
+  java.util.Map
+  (diff-similar [a b]
+    (diff-associative a b (set/union (keys a) (keys b)))))
+
+(defn diff
+  "Recursively compares a and b, returning a tuple of
+  [things-only-in-a things-only-in-b things-in-both].
+  Comparison rules:
+
+  * For equal a and b, return [nil nil a].
+  * Maps are subdiffed where keys match and values differ.
+  * Sets are never subdiffed.
+  * All sequential things are treated as associative collections
+    by their indexes, with results returned as vectors.
+  * Everything else (including strings!) is treated as
+    an atom and compared for equality."
+  {:added "1.3"}
+  [a b]
+  (if (= a b)
+    [nil nil a]
+    (if (= (equality-partition a) (equality-partition b))
+      (diff-similar a b)
+      (atom-diff a b))))
+  
diff --git a/src/babashka/impl/data.clj b/src/babashka/impl/data.clj
new file mode 100644
index 00000000..fd38dfa5
--- /dev/null
+++ b/src/babashka/impl/data.clj
@@ -0,0 +1,10 @@
+(ns babashka.impl.data
+  {:no-doc true}
+  (:require [babashka.impl.clojure.data :as data]
+            [sci.impl.namespaces :refer [copy-var]]
+            [sci.impl.vars :as vars]))
+
+(def data-ns (vars/->SciNamespace 'clojure.data nil))
+
+(def data-namespace
+  {'diff       (copy-var data/diff data-ns)})
diff --git a/src/babashka/main.clj b/src/babashka/main.clj
index e743497e..4afe6e32 100644
--- a/src/babashka/main.clj
+++ b/src/babashka/main.clj
@@ -6,7 +6,6 @@
    [babashka.impl.classes :as classes]
    [babashka.impl.classpath :as cp]
    [babashka.impl.clojure.core :as core :refer [core-extras]]
-   [babashka.impl.clojure.data :as data]
    [babashka.impl.clojure.java.io :refer [io-namespace]]
    [babashka.impl.clojure.java.shell :refer [shell-namespace]]
    [babashka.impl.clojure.main :as clojure-main :refer [demunge]]
@@ -15,6 +14,7 @@
    [babashka.impl.clojure.zip :refer [zip-namespace]]
    [babashka.impl.common :as common]
    [babashka.impl.curl :refer [curl-namespace]]
+   [babashka.impl.data :as data]
    [babashka.impl.features :as features]
    [babashka.impl.ordered :refer [ordered-map-ns]]
    [babashka.impl.pods :as pods]