debug NPE

gistfile1.txt

diff --git i/src/clj/clojure/core_deftype.clj w/src/clj/clojure/core_deftype.clj
index 97e14cc..eb98de8 100644
--- i/src/clj/clojure/core_deftype.clj
+++ w/src/clj/clojure/core_deftype.clj
@@ -50,6 +50,18 @@
              (drop-while seq? (next s)))
       ret)))

+(comment
+  (map deref
+    (into []
+      (for [i (range 20)]
+        (future
+          (dotimes [i 1000000]
+            (when (-> nil set (disj 'Object 'java.lang.Object) vec seq)
+              (throw (Exception.)))))))))
+
+(defn- spy [x]
+  (println "calling set with:" x) x)
+
 (defn- parse-opts+specs [opts+specs]
   (let [[opts specs] (parse-opts opts+specs)
         impls (parse-impls specs)
@@ -57,6 +69,8 @@
                                (:on (deref (resolve %)))
                                %)
                             (keys impls))
+                       seq
+                       spy
                        set
                        (disj 'Object 'java.lang.Object)
                        vec)
diff --git i/src/jvm/clojure/lang/PersistentVector.java w/src/jvm/clojure/lang/PersistentVector.java
index 9804a0b..e54a5a1 100644
--- i/src/jvm/clojure/lang/PersistentVector.java
+++ w/src/jvm/clojure/lang/PersistentVector.java
@@ -102,7 +102,20 @@ static public PersistentVector create(Iterable items){
     TransientVector ret = EMPTY.asTransient();
     while(iter.hasNext())
         ret = ret.conj(iter.next());
-    return ret.persistent();
+    PersistentVector retP = ret.persistent();
+    if (retP.count() != RT.count(items)) {
+        IFn println = RT.var("clojure.core", "println");
+        println.invoke("items:", items);
+        println.invoke("items class:", items.getClass().getName());
+        println.invoke("returned vector:", retP);
+        println.invoke("same as empty:" , items == PersistentHashSet.EMPTY);
+        // Prevent debug output getting munged with traceback
+        try {
+                       Thread.sleep(200);
+               } catch (InterruptedException e) {}
+        Util.sneakyThrow(new Exception("PersistentVector too long"));
[19:08][michael.blume@tcc-michael-4:~/workspace/clojure((3e7cb1a...) *)]$ g d | cat
diff --git i/src/clj/clojure/core_deftype.clj w/src/clj/clojure/core_deftype.clj
index 97e14cc..eb98de8 100644
--- i/src/clj/clojure/core_deftype.clj
+++ w/src/clj/clojure/core_deftype.clj
@@ -50,6 +50,18 @@
              (drop-while seq? (next s)))
       ret)))

+(comment
+  (map deref
+    (into []
+      (for [i (range 20)]
+        (future
+          (dotimes [i 1000000]
+            (when (-> nil set (disj 'Object 'java.lang.Object) vec seq)
+              (throw (Exception.)))))))))
+
+(defn- spy [x]
+  (println "calling set with:" x) x)
+
 (defn- parse-opts+specs [opts+specs]
   (let [[opts specs] (parse-opts opts+specs)
         impls (parse-impls specs)
@@ -57,6 +69,8 @@
                                (:on (deref (resolve %)))
                                %)
                             (keys impls))
+                       seq
+                       spy
                        set
                        (disj 'Object 'java.lang.Object)
                        vec)
diff --git i/src/jvm/clojure/lang/PersistentVector.java w/src/jvm/clojure/lang/PersistentVector.java
index 9804a0b..e54a5a1 100644
--- i/src/jvm/clojure/lang/PersistentVector.java
+++ w/src/jvm/clojure/lang/PersistentVector.java
@@ -102,7 +102,20 @@ static public PersistentVector create(Iterable items){
     TransientVector ret = EMPTY.asTransient();
     while(iter.hasNext())
         ret = ret.conj(iter.next());
-    return ret.persistent();
+    PersistentVector retP = ret.persistent();
+    if (retP.count() != RT.count(items)) {
+        IFn println = RT.var("clojure.core", "println");
+        println.invoke("items:", items);
+        println.invoke("items class:", items.getClass().getName());
+        println.invoke("returned vector:", retP);
+        println.invoke("same as empty:" , items == PersistentHashSet.EMPTY);
+        // Prevent debug output getting munged with traceback
+        try {
+			Thread.sleep(200);
+		} catch (InterruptedException e) {}
+        Util.sneakyThrow(new Exception("PersistentVector too long"));
+    }
+    return retP;
 }

 static public PersistentVector create(Object... items){