diff --git a/.idea/misc.xml b/.idea/misc.xml
index 89e54d4..9afac53 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -21,6 +21,7 @@
     <cargoProject FILE="$PROJECT_DIR$/lifetimes/Cargo.toml" />
     <cargoProject FILE="$PROJECT_DIR$/adder/Cargo.toml" />
     <cargoProject FILE="$PROJECT_DIR$/minigrep/Cargo.toml" />
+    <cargoProject FILE="$PROJECT_DIR$/closures/Cargo.toml" />
   </component>
   <component name="ComposerJsonPluginSettings">
     <unboundedVersionInspectionSettings>
diff --git a/.idea/rust.iml b/.idea/rust.iml
index eb9d073..06f6986 100644
--- a/.idea/rust.iml
+++ b/.idea/rust.iml
@@ -82,8 +82,13 @@
       <sourceFolder url="file://$MODULE_DIR$/minigrep/examples" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/minigrep/tests" isTestSource="true" />
       <sourceFolder url="file://$MODULE_DIR$/minigrep/benches" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/closures/src" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/closures/examples" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/closures/tests" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/closures/benches" isTestSource="true" />
       <excludeFolder url="file://$MODULE_DIR$/adder/target" />
       <excludeFolder url="file://$MODULE_DIR$/branches/target" />
+      <excludeFolder url="file://$MODULE_DIR$/closures/target" />
       <excludeFolder url="file://$MODULE_DIR$/ctof/target" />
       <excludeFolder url="file://$MODULE_DIR$/enums/target" />
       <excludeFolder url="file://$MODULE_DIR$/errors/target" />
diff --git a/.idea/workspace.xml b/.idea/workspace.xml
index 54a3b77..8270e60 100644
--- a/.idea/workspace.xml
+++ b/.idea/workspace.xml
@@ -13,30 +13,12 @@
     <option name="LAST_RESOLUTION" value="IGNORE" />
   </component>
   <component name="FileEditorManager">
-    <leaf SIDE_TABS_SIZE_LIMIT_KEY="300">
+    <leaf>
       <file pinned="false" current-in-tab="true">
-        <entry file="file://$PROJECT_DIR$/minigrep/src/main.rs">
+        <entry file="file://$PROJECT_DIR$/closures/src/main.rs">
           <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="320">
-              <caret line="20" lean-forward="true" selection-start-line="20" selection-end-line="20" />
-            </state>
-          </provider>
-        </entry>
-      </file>
-      <file pinned="false" current-in-tab="false">
-        <entry file="file://$PROJECT_DIR$/minigrep/src/lib.rs">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="517">
-              <caret line="33" column="6" selection-start-line="33" selection-start-column="6" selection-end-line="33" selection-end-column="6" />
-            </state>
-          </provider>
-        </entry>
-      </file>
-      <file pinned="false" current-in-tab="false">
-        <entry file="file://$PROJECT_DIR$/minigrep/poem.txt">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="128">
-              <caret line="8" column="19" selection-start-line="8" selection-start-column="19" selection-end-line="8" selection-end-column="19" />
+            <state relative-caret-position="1136">
+              <caret line="71" lean-forward="true" selection-start-line="71" selection-end-line="71" />
             </state>
           </provider>
         </entry>
@@ -53,9 +35,11 @@
   <component name="FindInProjectRecents">
     <findStrings>
       <find>ftoc</find>
+      <find>expensive_closure(intensity)</find>
     </findStrings>
     <replaceStrings>
       <replace>f_to_c</replace>
+      <replace>expensive_result.value(intensity)</replace>
     </replaceStrings>
   </component>
   <component name="Git.Settings">
@@ -97,6 +81,7 @@
         <option value="$PROJECT_DIR$/minigrep/poem.txt" />
         <option value="$PROJECT_DIR$/minigrep/src/lib.rs" />
         <option value="$PROJECT_DIR$/minigrep/src/main.rs" />
+        <option value="$PROJECT_DIR$/closures/src/main.rs" />
       </list>
     </option>
   </component>
@@ -106,11 +91,11 @@
     <annotation-enable>false</annotation-enable>
     <other-services-enabled>false</other-services-enabled>
   </component>
-  <component name="ProjectFrameBounds" extendedState="6">
-    <option name="x" value="1680" />
-    <option name="y" value="371" />
-    <option name="width" value="1050" />
-    <option name="height" value="876" />
+  <component name="ProjectFrameBounds">
+    <option name="x" value="1920" />
+    <option name="y" value="-438" />
+    <option name="width" value="1080" />
+    <option name="height" value="1897" />
   </component>
   <component name="ProjectLevelVcsManager" settingsEditedManually="true">
     <ConfirmationsSetting value="1" id="Add" />
@@ -127,22 +112,10 @@
               <item name="rust" type="3d21c010:ScopeViewTreeModel$ProjectNode" />
               <item name="rust" type="2674bda8:ScopeViewTreeModel$GroupNode" />
             </path>
-            <path>
-              <item name="rust" type="3d21c010:ScopeViewTreeModel$ProjectNode" />
-              <item name="rust" type="2674bda8:ScopeViewTreeModel$GroupNode" />
-              <item name="minigrep" type="9f88c78c:ScopeViewTreeModel$FileNode" />
-            </path>
-            <path>
-              <item name="rust" type="3d21c010:ScopeViewTreeModel$ProjectNode" />
-              <item name="rust" type="2674bda8:ScopeViewTreeModel$GroupNode" />
-              <item name="minigrep" type="9f88c78c:ScopeViewTreeModel$FileNode" />
-              <item name="src" type="9f88c78c:ScopeViewTreeModel$FileNode" />
-            </path>
           </expand>
           <select />
         </subPane>
       </pane>
-      <pane id="PackagesPane" />
       <pane id="ProjectPane">
         <subPane>
           <expand>
@@ -165,11 +138,12 @@
           <select />
         </subPane>
       </pane>
+      <pane id="PackagesPane" />
     </panes>
   </component>
   <component name="PropertiesComponent">
     <property name="JavaScriptWeakerCompletionTypeGuess" value="true" />
-    <property name="com.android.tools.idea.instantapp.provision.ProvisionBeforeRunTaskProvider.myTimeStamp" value="1548969593161" />
+    <property name="com.android.tools.idea.instantapp.provision.ProvisionBeforeRunTaskProvider.myTimeStamp" value="1549047706729" />
     <property name="javascript.nodejs.core.library.configured.version" value="7.1.0" />
     <property name="js.eslint.eslintPackage" value="$USER_HOME$/.yarn-config/global/node_modules/.bin/eslint" />
     <property name="js.eslint.nodeInterpreter" value="project" />
@@ -183,7 +157,7 @@
     <property name="nodejs_npm_path_reset_for_default_project" value="true" />
     <property name="org.rust.cargo.project.model.PROJECT_DISCOVERY" value="true" />
     <property name="run.code.analysis.last.selected.profile" value="pProject Default" />
-    <property name="settings.editor.selected.configurable" value="reference.settingsdialog.IDE.editor.colors.Language Defaults" />
+    <property name="settings.editor.selected.configurable" value="reference.settingsdialog.IDE.editor.colors.General" />
   </component>
   <component name="RunDashboard">
     <option name="ruleStates">
@@ -197,7 +171,7 @@
       </list>
     </option>
   </component>
-  <component name="RunManager" selected="Cargo Command.Test lib::tests">
+  <component name="RunManager" selected="Cargo Command.Run closures">
     <configuration name="&lt;template&gt;" type="TestNG" default="true" selected="false">
       <option name="MAIN_CLASS_NAME" />
       <option name="VM_PARAMETERS" value="-ea" />
@@ -216,13 +190,13 @@
         <option name="Make" enabled="true" />
       </method>
     </configuration>
-    <configuration name="Run lifetimes" type="CargoCommandRunConfiguration" factoryName="Cargo Command" temporary="true">
+    <configuration name="Run closures" type="CargoCommandRunConfiguration" factoryName="Cargo Command" temporary="true">
       <option name="channel" value="DEFAULT" />
-      <option name="command" value="run --package lifetimes --bin lifetimes" />
+      <option name="command" value="run --package closures --bin closures" />
       <option name="allFeatures" value="false" />
       <option name="nocapture" value="false" />
       <option name="backtrace" value="SHORT" />
-      <option name="workingDirectory" value="file://$PROJECT_DIR$/lifetimes" />
+      <option name="workingDirectory" value="file://$PROJECT_DIR$/closures" />
       <envs />
       <method v="2" />
     </configuration>
@@ -275,11 +249,11 @@
     </configuration>
     <recent_temporary>
       <list>
+        <item itemvalue="Cargo Command.Run closures" />
         <item itemvalue="Cargo Command.Test lib::tests" />
         <item itemvalue="Cargo Command.Test tests::greater_than_100" />
         <item itemvalue="Cargo Command.Test tests::greeting_contains_name" />
         <item itemvalue="Cargo Command.Test tests::it_works" />
-        <item itemvalue="Cargo Command.Run lifetimes" />
       </list>
     </recent_temporary>
   </component>
@@ -304,11 +278,11 @@
     </history-entry>
   </component>
   <component name="ToolWindowManager">
-    <frame x="1680" y="-410" width="1050" height="1657" extended-state="6" />
+    <frame x="1920" y="-438" width="1080" height="1897" extended-state="6" />
     <editor active="true" />
     <layout>
-      <window_info content_ui="combo" id="Project" order="0" sideWeight="0.49710983" visible="true" weight="0.26141885" />
-      <window_info id="Structure" order="1" sideWeight="0.50289017" side_tool="true" visible="true" weight="0.26141885" />
+      <window_info active="true" content_ui="combo" id="Project" order="0" sideWeight="0.49692565" visible="true" weight="0.2540132" />
+      <window_info id="Structure" order="1" sideWeight="0.50307435" side_tool="true" visible="true" weight="0.2540132" />
       <window_info id="Image Layers" order="2" />
       <window_info id="Designer" order="3" />
       <window_info id="Capture Tool" order="4" />
@@ -316,7 +290,7 @@
       <window_info id="Cargo" order="6" sideWeight="0.49791494" weight="0.3286119" />
       <window_info anchor="bottom" id="Message" order="0" />
       <window_info anchor="bottom" id="Find" order="1" weight="0.32979318" />
-      <window_info anchor="bottom" id="Run" order="2" weight="0.29761136" />
+      <window_info anchor="bottom" id="Run" order="2" weight="0.29737285" />
       <window_info anchor="bottom" id="Debug" order="3" weight="0.4" />
       <window_info anchor="bottom" id="Cvs" order="4" weight="0.25" />
       <window_info anchor="bottom" id="Inspection" order="5" weight="0.4" />
@@ -324,7 +298,7 @@
       <window_info anchor="bottom" id="Docker" order="7" show_stripe_button="false" />
       <window_info anchor="bottom" id="Version Control" order="8" />
       <window_info anchor="bottom" id="Inspection Results" order="9" weight="0.32979318" />
-      <window_info active="true" anchor="bottom" id="Terminal" order="10" visible="true" weight="0.32989025" />
+      <window_info anchor="bottom" id="Terminal" order="10" weight="0.28563443" />
       <window_info anchor="bottom" id="Event Log" order="11" side_tool="true" />
       <window_info anchor="right" id="Commander" order="0" weight="0.4" />
       <window_info anchor="right" id="Ant Build" order="1" weight="0.25" />
@@ -627,5 +601,12 @@
         </state>
       </provider>
     </entry>
+    <entry file="file://$PROJECT_DIR$/closures/src/main.rs">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="1136">
+          <caret line="71" lean-forward="true" selection-start-line="71" selection-end-line="71" />
+        </state>
+      </provider>
+    </entry>
   </component>
 </project>
\ No newline at end of file
diff --git a/closures/Cargo.toml b/closures/Cargo.toml
new file mode 100644
index 0000000..bef6418
--- /dev/null
+++ b/closures/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "closures"
+version = "0.1.0"
+authors = ["Timothy Warren <twarren@nabancard.com>"]
+edition = "2018"
+
+[dependencies]
diff --git a/closures/src/main.rs b/closures/src/main.rs
new file mode 100644
index 0000000..f616792
--- /dev/null
+++ b/closures/src/main.rs
@@ -0,0 +1,71 @@
+use std::thread;
+use std::time::Duration;
+
+// @TODO: use a hashmap to memoize based on teh argument passed
+// @TODO:  make more generic, to accept different types of arguments
+struct Cacher<T>
+    where T: Fn(u32) -> u32
+{
+    calculation: T,
+    value: Option<u32>,
+}
+
+impl<T> Cacher<T>
+    where T: Fn(u32) -> u32
+{
+    fn new(calculation: T) -> Cacher<T> {
+        Cacher {
+            calculation,
+            value: None,
+        }
+    }
+
+    fn value(&mut self, arg: u32) -> u32 {
+        match self.value {
+            Some(v) => v,
+            None => {
+                let v = (self.calculation)(arg);
+                self.value = Some(v);
+                v
+            },
+        }
+    }
+}
+
+fn generate_workout(intensity: u32, random_number: u32) {
+    let mut expensive_result = Cacher::new(|num| {
+        println!("calculating slowly...");
+        thread::sleep(Duration::from_secs(2));
+        num
+    });
+
+    if intensity < 25 {
+        println!(
+            "Today do {} pushups!",
+            expensive_result.value(intensity)
+        );
+        println!(
+            "Next, do {} situps!",
+            expensive_result.value(intensity)
+        );
+    } else {
+        if random_number == 3 {
+            println!("Take a break today! Remember to stay hydrated!");
+        } else {
+            println!(
+                "Today, run for {} minutes!",
+                expensive_result.value(intensity)
+            );
+        }
+    }
+}
+
+fn main() {
+    let simulated_user_specified_value = 10;
+    let simulated_random_number = 7;
+
+    generate_workout(
+        simulated_user_specified_value,
+        simulated_random_number
+    );
+}