diff --git a/elm-todo/Todo.elm b/elm-todo/Todo.elm
index 3a07b24..dbe01a4 100755
--- a/elm-todo/Todo.elm
+++ b/elm-todo/Todo.elm
@@ -45,7 +45,6 @@ type alias Model =
 type alias Entry =
     { description : String
     , completed : Bool
-    , editing : Bool
     , id : Int
     }
 
@@ -62,7 +61,6 @@ newEntry : String -> Int -> Entry
 newEntry desc id =
     { description = desc
     , completed = False
-    , editing = False
     , id = id
     }
 
@@ -76,7 +74,6 @@ to them.
 -}
 type Msg
     = UpdateNewEntryField String
-    | EditingEntry Int Bool
     | UpdateEntry Int String
     | Add
     | Delete Int
@@ -102,18 +99,6 @@ update msg model =
         UpdateNewEntryField str ->
             { model | newEntryField = str }
 
-        EditingEntry id isEditing ->
-            let
-                updateEntry t =
-                    if t.id == id then
-                        { t | editing = isEditing }
-                    else
-                        t
-
-                focus =
-                    Dom.focus ("todo-" ++ toString id)
-            in
-                { model | entries = List.map updateEntry model.entries }
 
         UpdateEntry id task ->
             let
@@ -229,7 +214,7 @@ viewKeyedEntry todo =
 viewEntry : Entry -> Html Msg
 viewEntry todo =
     li
-        [ classList [ ( "completed", todo.completed ), ( "editing", todo.editing ) ] ]
+        [ classList [ ( "completed", todo.completed ) ] ]
         [ div
             [ class "view" ]
             [ input
@@ -240,7 +225,7 @@ viewEntry todo =
                 ]
                 []
             , label
-                [ onDoubleClick (EditingEntry todo.id True) ]
+                []
                 [ text todo.description ]
             , button
                 [ class "destroy"
@@ -254,8 +239,6 @@ viewEntry todo =
             , name "title"
             , id ("todo-" ++ toString todo.id)
             , onInput (UpdateEntry todo.id)
-            , onBlur (EditingEntry todo.id False)
-            , onEnter (EditingEntry todo.id False)
             ]
             []
         ]
diff --git a/ruby-todo/lib/engine.rb b/ruby-todo/lib/engine.rb
index a257c20..500747c 100644
--- a/ruby-todo/lib/engine.rb
+++ b/ruby-todo/lib/engine.rb
@@ -4,9 +4,10 @@ def self.run(*args)
   end
 
   def self.run_with_history(model, messages)
+    model0 = model
     messages.map do |msg|
-      msg.apply_to(model)
-      model
+      model0 = msg.apply_to(model0)
+      model0
     end
   end
 end
diff --git a/ruby-todo/lib/messages.rb b/ruby-todo/lib/messages.rb
index abe85de..3cb28ef 100644
--- a/ruby-todo/lib/messages.rb
+++ b/ruby-todo/lib/messages.rb
@@ -1,14 +1,13 @@
 module Msg
-
   class Add
     def apply_to(model)
-      unless model.new_entry_field.blank?
-        model.entries << Entry.new(
+      model0 = model.dup    # Steven Roach told me about .dup
+      unless model0.new_entry_field.blank?
+        model0.entries << Entry.new(
           description: model.new_entry_field,
           id: model.next_id)
       end
-      model.next_id += 1
-      model.new_entry_field = ""
+      Model.new(next_id: model.next_id + 1, entries: model0.entries, new_entry_field: "")
     end
   end
 
@@ -17,10 +16,10 @@ def initialize(str)
       @str = str
     end
 
-    attr_reader :str 
+    attr_reader :str
 
     def apply_to(model)
-      model.new_entry_field = str
+      Model.new(next_id: model.next_id, entries: model.entries, new_entry_field: str)
     end
   end
 
@@ -29,14 +28,18 @@ def initialize(id, is_completed)
       @id, @is_completed = id, is_completed
     end
 
-    attr_reader :id, :is_completed 
+    attr_reader :id, :is_completed
 
     def apply_to(model)
+      entries0 = []
       model.entries.each do |entry|
         if entry.id == id
-          entry.completed = is_completed
+          entries0 << Entry.new(id: entry.id, description: entry.description, completed: is_completed)
+        else
+          entries0 << entry.dup
         end
       end
+      Model.new(entries: entries0, new_entry_field: model.new_entry_field, next_id: model.next_id)
     end
   end
 
@@ -45,16 +48,20 @@ def initialize(id)
       @id = id
     end
 
-    attr_reader :id 
+    attr_reader :id
 
     def apply_to(model)
-      model.entries.reject! { |e| e.id == id }
+      entries1 = model.entries.dup
+      entries1.reject! { |e| e.id == id }
+      Model.new(entries: entries1, new_entry_field: model.new_entry_field, next_id: model.next_id)
     end
   end
 
   class DeleteAllCompleted
     def apply_to(model)
-      model.entries.reject!(&:completed)
+      entries2 = model.entries.dup
+      entries2.reject!(&:completed)
+      Model.new(entries: entries2, new_entry_field: model.new_entry_field, next_id: model.next_id)
     end
   end
 
diff --git a/ruby-todo/lib/model.rb b/ruby-todo/lib/model.rb
index 75a6085..bdfccc1 100644
--- a/ruby-todo/lib/model.rb
+++ b/ruby-todo/lib/model.rb
@@ -5,7 +5,7 @@ def initialize(entries: [], new_entry_field: "", next_id: nil)
       (entries.lazy.map(&:id).max || -1) + 1
   end
 
-  attr_accessor :entries, :new_entry_field, :next_id
+  attr_reader :entries, :new_entry_field, :next_id
 
   def ==(other)
     !other.nil? &&
diff --git a/ruby-todo/test/todo_test.rb b/ruby-todo/test/todo_test.rb
index f7436c7..471fc7e 100644
--- a/ruby-todo/test/todo_test.rb
+++ b/ruby-todo/test/todo_test.rb
@@ -121,7 +121,7 @@
           Entry.new(id: 0, description: "go forward in time", completed: false)
       ]),
       Model.new(next_id: 3, new_entry_field: "", entries: [
-          Entry.new(id: 0, description: "go forward in time", completed: false), 
+          Entry.new(id: 0, description: "go forward in time", completed: false),
           Entry.new(id: 2, description: "delete this item", completed: false)
       ]),
       Model.new(next_id: 3, new_entry_field: "", entries: [
@@ -134,19 +134,19 @@
           Entry.new(id: 0, description: "go forward in time", completed: false)
       ]),
       Model.new(next_id: 4, new_entry_field: "", entries: [
-          Entry.new(id: 0, description: "go forward in time", completed: false), 
+          Entry.new(id: 0, description: "go forward in time", completed: false),
           Entry.new(id: 3, description: "go backward in time", completed: false)
       ]),
       Model.new(next_id: 4, new_entry_field: "", entries: [
-          Entry.new(id: 0, description: "go forward in time", completed: true), 
+          Entry.new(id: 0, description: "go forward in time", completed: true),
           Entry.new(id: 3, description: "go backward in time", completed: false)
       ]),
       Model.new(next_id: 4, new_entry_field: "", entries: [
-          Entry.new(id: 0, description: "go forward in time", completed: true), 
+          Entry.new(id: 0, description: "go forward in time", completed: true),
           Entry.new(id: 3, description: "go backward in time", completed: true)
       ]),
       Model.new(next_id: 4, new_entry_field: "", entries: [
-          Entry.new(id: 0, description: "go forward in time", completed: true), 
+          Entry.new(id: 0, description: "go forward in time", completed: true),
           Entry.new(id: 3, description: "go backward in time", completed: false)
       ]),
       Model.new(next_id: 4, new_entry_field: "", entries: [
diff --git a/swift-todo/Sources/Todo/Engine.swift b/swift-todo/Sources/Todo/Engine.swift
index e3b14a7..8608c5f 100644
--- a/swift-todo/Sources/Todo/Engine.swift
+++ b/swift-todo/Sources/Todo/Engine.swift
@@ -13,9 +13,10 @@ struct Engine {
     }
 
     static func runWithHistory(on model: Model, applying messages: [Message]) -> [Model] {
+        var model1 = model
         return messages.map { message in
-          message.apply(to: model)
-          return model
+          model1 = message.apply(to: model1)
+          return model1
         }
     }
 }
diff --git a/swift-todo/Sources/Todo/Message.swift b/swift-todo/Sources/Todo/Message.swift
index 92dd868..a07d061 100644
--- a/swift-todo/Sources/Todo/Message.swift
+++ b/swift-todo/Sources/Todo/Message.swift
@@ -14,30 +14,35 @@ enum Message {
     case delete(Int)
     case deleteAllCompleted
 
-    func apply(to model: Model) {
+    func apply(to model: Model) -> Model {
+        var model1 = model
         switch(self) {
             case .add:
-                if !model.newEntryField.isBlank() {
-                    model.entries.append(Entry(id: model.nextID, description: model.newEntryField))
+                if !model1.newEntryField.isBlank() {
+                    model1.entries.append(Entry(id: model.nextID, description: model.newEntryField))
                 }
-                model.nextID += 1
-                model.newEntryField = ""
+                return Model(nextID: model.nextID + 1, entries: model1.entries)
 
             case .updateNewEntryField(let str):
-                model.newEntryField = str
+                model1.newEntryField = str
+                return model1
 
             case .check(let id, let isCompleted):
-                for entry in model.entries {
-                    if(entry.id == id) {
-                        entry.completed = isCompleted
+                for i in 0..<(model1.entries.count){
+                    if model1.entries[i].id == id{
+                        let entry0 = Entry(id: model1.entries[i].id, description: model1.entries[i].description, completed: isCompleted)
+                        model1.entries[i] = entry0
                     }
                 }
+                return model1
 
             case .delete(let id):
-                model.entries.remove { $0.id == id }
+                model1.entries.remove { $0.id == id }
+                return model1
 
             case .deleteAllCompleted:
-                model.entries.remove { $0.completed }
+                model1.entries.remove { $0.completed }
+                return model1
         }
     }
 }
diff --git a/swift-todo/Sources/Todo/Model.swift b/swift-todo/Sources/Todo/Model.swift
index 1cca801..d50d863 100644
--- a/swift-todo/Sources/Todo/Model.swift
+++ b/swift-todo/Sources/Todo/Model.swift
@@ -1,4 +1,4 @@
-class Model {
+struct Model {
     var entries: [Entry]
     var newEntryField: String
     var nextID: Int
@@ -11,7 +11,7 @@ class Model {
     }
 }
 
-class Entry {
+struct Entry {
     var id: Int
     var description: String
     var completed: Bool
diff --git a/swift-todo/Tests/TodoTests/TodoTests.swift b/swift-todo/Tests/TodoTests/TodoTests.swift
index 9220517..7346f27 100644
--- a/swift-todo/Tests/TodoTests/TodoTests.swift
+++ b/swift-todo/Tests/TodoTests/TodoTests.swift
@@ -77,7 +77,7 @@ class TodoTests: XCTestCase {
          XCTAssertEqual([11], newModel.entries.map { $0.id })
      }
 
-/*
+
      func testTimeTravel() {
         let actualHistory = Engine.runWithHistory(on: Model(), applying: [
              .updateNewEntryField("go forward in time"),
@@ -145,6 +145,6 @@ class TodoTests: XCTestCase {
              XCTAssertEqual(expected, actual, "History mismatch at step \(index)")
          }
     }
-*/
+
 
 }