diff --git a/propeller.iml b/propeller.iml
index f20aa6f..6d18148 100644
--- a/propeller.iml
+++ b/propeller.iml
@@ -5,9 +5,9 @@
     <output-test url="file://$MODULE_DIR$/target/classes" />
     <exclude-output />
     <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/dev-resources" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/resources" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
-      <sourceFolder url="file://$MODULE_DIR$/dev-resources" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/test" isTestSource="true" />
       <excludeFolder url="file://$MODULE_DIR$/target" />
     </content>
diff --git a/src/propeller/push/interpreter.cljc b/src/propeller/push/interpreter.cljc
index 0e01fb2..0735c2e 100755
--- a/src/propeller/push/interpreter.cljc
+++ b/src/propeller/push/interpreter.cljc
@@ -37,10 +37,17 @@
                                       (name instruction))))))))
 
 (defn interpret-program
-  "Runs the given problem starting with the stacks in start-state."
+  "Runs the given problem starting with the stacks in start-state. If the
+  start-state includes the key :keep-history with a truthy value, then
+  the returned state will include the key :history with a value that is a
+  vector containing all states prior to the final state."
   [program start-state step-limit]
-  (loop [state (assoc start-state :exec program :step 1)]
+  (loop [state (assoc start-state :exec program :step 1)
+         history []]
     (if (or (empty? (:exec state))
             (> (:step state) step-limit))
-      state
-      (recur (update (interpret-one-step state) :step inc)))))
+      (if (:keep-history state)
+        (assoc state :history history)
+        state)
+      (recur (update (interpret-one-step state) :step inc)
+             (when (:keep-history state) (conj history state))))))
diff --git a/src/propeller/session.cljc b/src/propeller/session.cljc
index c9f9e22..d949528 100755
--- a/src/propeller/session.cljc
+++ b/src/propeller/session.cljc
@@ -10,9 +10,12 @@
             [propeller.push.state :as state]
             [propeller.push.utils.helpers :refer [get-stack-instructions]]))
 
-;#_(interpreter/interpret-program
-;    '(1 2 :integer_add) state/empty-state 1000)
-;
+#_(interpreter/interpret-program
+    '(1 2 :integer_add) state/empty-state 1000)
+
+#_(interpreter/interpret-program
+    '(1 2 :integer_add) (assoc state/empty-state :keep-history true) 1000)
+
 ;#_(interpreter/interpret-program
 ;    '(3 3 :integer_eq :exec_if (1 "yes") (2 "no"))
 ;    state/empty-state