diff --git a/README.md b/README.md
index e68f99d..d6fa57d 100644
--- a/README.md
+++ b/README.md
@@ -92,7 +92,8 @@ update msg model =
 - **Install.FieldInTypeAlias**: Add a field to a specified type alias in a specified module. For more details, see the [docs](https://package.elm-lang.org/packages/jxxcarlson/elm-review-codeinstaller/latest/Install-FieldInTypeAlias).
 - **Install.Initializer**: Add a field to the body of an initializer function where the return value is of the form `( Model, Cmd msg )`. For more details, see the [docs](https://package.elm-lang.org/packages/jxxcarlson/elm-review-codeinstaller/latest/Install-Initializer).
 - **Install.TypeVariant**: Add a variant to a specified type in a specified module. For more details, see the [docs](https://package.elm-lang.org/packages/jxxcarlson/elm-review-codeinstaller/latest/Install-TypeVariant).
-- **Install.Function**: Replace a function in a given module with a new implementation or add that function definition if it is not present in the module. For more details, see the [docs](https://package.elm-lang.org/packages/jxxcarlson/elm-review-codeinstaller/latest/Install-Function).
+- **Install.Function.ReplaceFunction**: Replace a function in a given module with a new implementation. For more details, see the [docs](https://package.elm-lang.org/packages/jxxcarlson/elm-review-codeinstaller/latest/Install-Function-ReplaceFunction).
+- **Install.Function.InsertFunction**: Add a function in a given module if it is not present. For more details, see the [docs](https://package.elm-lang.org/packages/jxxcarlson/elm-review-codeinstaller/latest/Install-Function-InsertFunction).
 - **Install.Import**: Add import statements to a given module. For more details, see the [docs](https://package.elm-lang.org/packages/jxxcarlson/elm-review-codeinstaller/latest/Install-Import).
 
 ## Try it out
diff --git a/elm.json b/elm.json
index 0fb1aa1..9578612 100644
--- a/elm.json
+++ b/elm.json
@@ -9,7 +9,8 @@
         "Install.FieldInTypeAlias",
         "Install.Initializer",
         "Install.TypeVariant",
-        "Install.Function",
+        "Install.Function.InsertFunction",
+        "Install.Function.ReplaceFunction",
         "Install.Import",
         "Install.Type"
     ],
diff --git a/preview/src/ReviewConfig.elm b/preview/src/ReviewConfig.elm
index e4a66c8..8e6c2c1 100644
--- a/preview/src/ReviewConfig.elm
+++ b/preview/src/ReviewConfig.elm
@@ -11,34 +11,36 @@ when inside the directory containing this file.
 
 -}
 
-import Install.Import
-import Install.TypeVariant
+import Install.ClauseInCase
 import Install.FieldInTypeAlias
-import Install.Type
+import Install.Function.InsertFunction
+import Install.Function.ReplaceFunction
+import Install.Import
 import Install.Initializer
-import Install.ClauseInCase
-import Install.Function
+import Install.Type
+import Install.TypeVariant
 import Review.Rule exposing (Rule)
 
-config = config1
+
+config =
+    config1
 
 
 config1 : List Rule
 config1 =
-    [
-       Install.TypeVariant.makeRule "Types" "ToBackend" "CounterReset"
-     , Install.TypeVariant.makeRule "Types" "FrontendMsg" "Reset"
-     , Install.ClauseInCase.init "Frontend" "update" "Reset" "( { model | counter = 0 }, sendToBackend CounterReset )"
+    [ Install.TypeVariant.makeRule "Types" "ToBackend" "CounterReset"
+    , Install.TypeVariant.makeRule "Types" "FrontendMsg" "Reset"
+    , Install.ClauseInCase.init "Frontend" "update" "Reset" "( { model | counter = 0 }, sendToBackend CounterReset )"
         |> Install.ClauseInCase.withInsertAfter "Increment"
         |> Install.ClauseInCase.makeRule
-     , Install.ClauseInCase.init "Backend" "updateFromFrontend" "CounterReset" "( { model | counter = 0 }, broadcast (CounterNewValue 0 clientId) )"
+    , Install.ClauseInCase.init "Backend" "updateFromFrontend" "CounterReset" "( { model | counter = 0 }, broadcast (CounterNewValue 0 clientId) )"
         |> Install.ClauseInCase.makeRule
-     , Install.Function.init "Frontend" "view" viewFunction |>Install.Function.makeRule
-
+    , Install.Function.ReplaceFunction.init "Frontend" "view" viewFunction |> Install.Function.ReplaceFunction.makeRule
     ]
 
 
-viewFunction = """view model =
+viewFunction =
+    """view model =
     Html.div [ style "padding" "50px" ]
         [ Html.button [ onClick Increment ] [ text "+" ]
         , Html.div [ style "padding" "10px" ] [ Html.text (String.fromInt model.counter) ]
@@ -47,7 +49,9 @@ viewFunction = """view model =
         , Html.button [ onClick Reset ] [ text "Reset" ]
         ]"""
 
-viewFunction2 = """view model =
+
+viewFunction2 =
+    """view model =
 Html.div [ style "padding" "50px" ]
     [ Html.button [ onClick Increment ] [ text "+" ]
     , Html.div [ style "padding" "10px" ] [ Html.text (String.fromInt model.counter) ]
@@ -56,7 +60,9 @@ Html.div [ style "padding" "50px" ]
     , Html.button [ onClick Reset ] [ text "Reset" ]
     ]"""
 
-viewFunction3 = """view model =
+
+viewFunction3 =
+    """view model =
   Html.div [ style "padding" "50px" ]
     [ Html.button [ onClick Increment ] [ text "+" ]
     , Html.div [ style "padding" "10px" ] [ Html.text (String.fromInt model.counter) ]
@@ -66,142 +72,160 @@ viewFunction3 = """view model =
     ]"""
 
 
-
 config2 : List Rule
 config2 =
-    [
-     -- TYPES
-           Install.Type.makeRule "Types" "SignInState" [ "SignedOut", "SignUp", "SignedIn" ]
-         , Install.Type.makeRule "Types" "BackendDataStatus" [ "Sunny", "LoadedBackendData" ]
-     -- TYPES IMPORTS
-          , Install.Import.initSimple "Types" ["Auth.Common", "MagicLink.Types", "User", "Session",  "Dict", "AssocList"] |>Install.Import.makeRule
-          , Install.Import.init "Types" [{moduleToImport = "Url", alias_ = Nothing, exposedValues = Just ["Url"] }] |>Install.Import.makeRule
-            -- Type Frontend, MagicLink
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "authFlow : Auth.Common.Flow"
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "authRedirectBaseUrl : Url"
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "signinForm : MagicLink.Types.SigninForm"
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "loginErrorMessage : Maybe String"
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "signInStatus : MagicLink.Types.SignInStatus"
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "currentUserData : Maybe User.LoginData"
-          -- Type Frontend, User
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "currentUser : Maybe User.User"
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "signInState : SignInState"
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "realname : String"
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "username : String"
-          , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "email : String"
-          -- Type BackendModel
-          , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "pendingAuths : Dict Lamdera.SessionId Auth.Common.PendingAuth"
-          , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "pendingEmailAuths : Dict Lamdera.SessionId Auth.Common.PendingEmailAuth"
-          , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "sessions : Dict SessionId Auth.Common.UserInfo"
-          , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "secretCounter : Int"
-          , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "sessionDict : AssocList.Dict SessionId String"
-          , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "pendingLogins: MagicLink.Types.PendingLogins"
-          , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "log : MagicLink.Types.Log"
-          , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "users: Dict.Dict User.EmailString User.User"
-          , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "userNameToEmailString : Dict.Dict User.Username User.EmailString"
-          , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "sessionInfo : Session.SessionInfo"
-        -- Type ToBackend
-          , Install.TypeVariant.makeRule "Types" "ToBackend" "AuthToBackend Auth.Common.ToBackend"
-          , Install.TypeVariant.makeRule "Types" "ToBackend" "AddUser String String String"
-          , Install.TypeVariant.makeRule "Types" "ToBackend" "RequestSignup String String String"
-        -- Type BackendMsg
-          , Install.TypeVariant.makeRule "Types" "BackendMsg" "AuthBackendMsg Auth.Common.BackendMsg"
-          , Install.TypeVariant.makeRule "Types" "BackendMsg" "AutoLogin SessionId User.LoginData"
-        -- Type ToFrontend
-          , Install.TypeVariant.makeRule "Types" "ToFrontend" "AuthToFrontend Auth.Common.ToFrontend"
-          , Install.TypeVariant.makeRule "Types" "ToFrontend" "AuthSuccess Auth.Common.UserInfo"
-          , Install.TypeVariant.makeRule "Types" "ToFrontend" "UserInfoMsg (Maybe Auth.Common.UserInfo)"
-          , Install.TypeVariant.makeRule "Types" "ToFrontend" "CheckSignInResponse (Result BackendDataStatus User.LoginData)"
-          , Install.TypeVariant.makeRule "Types" "ToFrontend" "GetLoginTokenRateLimited"
-          , Install.TypeVariant.makeRule "Types" "ToFrontend" "RegistrationError String"
-          , Install.TypeVariant.makeRule "Types" "ToFrontend" "SignInError String"
-          , Install.TypeVariant.makeRule "Types" "ToFrontend" "UserSignedIn (Maybe User.User)"
-          -- Initialize BackendModel
-          , Install.Initializer.makeRule "Backend" "init" "users" "Dict.empty"
-          , Install.Initializer.makeRule "Backend" "init" "sessions" "Dict.empty"
-          , Install.Initializer.makeRule "Backend" "init" "time" "Time.millisToPosix 0"
-          , Install.Initializer.makeRule "Backend" "init" "time" "Time.millisToPosix 0"
-          , Install.Initializer.makeRule "Backend" "init" "randomAtmosphericNumbers" "Nothing"
-          , Install.Initializer.makeRule "Backend" "init" "localUuidData" "Dict.empty"
-          , Install.Initializer.makeRule "Backend" "init" "pendingAuths" "Nothing"
-          , Install.Initializer.makeRule "Backend" "init" "localUuidData" "Nothing"
-          , Install.Initializer.makeRule "Backend" "init" "secretCounter" "0"
-          , Install.Initializer.makeRule "Backend" "init" "pendingAuths" "Dict.empty"
-          , Install.Initializer.makeRule "Backend" "init" "pendingEmailAuths" "Dict.empty"
-          , Install.Initializer.makeRule "Backend" "init" "sessionDict" "AssocList.empty"
-          , Install.Initializer.makeRule "Backend" "init" "sessionDict" "AssocList.empty"
-          , Install.Initializer.makeRule "Backend" "init" "log" "[]"
-          -- Backend import
-          , Install.Import.initSimple "Backend"
-             ["Auth.Common", "AssocList", "Auth.Flow" , "Dict", "Helper",  "LocalUUID",
-               "MagicLink.Auth", "Process", "Task", "Time", "User"]
-               |>Install.Import.makeRule
-          , Install.Import.init "Backend" [{moduleToImport = "Lamdera", alias_ = Nothing, exposedValues = Just ["ClientId", "SessionId"]}] |>Install.Import.makeRule
-          ---
-          , Install.ClauseInCase.init
-             "Frontend" "updateFromBacked"
-             "AuthToFrontend authToFrontendMsg"
-             "MagicLink.Auth.updateFromBackend authToFrontendMsg model"
-                  |> Install.ClauseInCase.makeRule
-
+    [ -- TYPES
+      Install.Type.makeRule "Types" "SignInState" [ "SignedOut", "SignUp", "SignedIn" ]
+    , Install.Type.makeRule "Types" "BackendDataStatus" [ "Sunny", "LoadedBackendData" ]
+
+    -- TYPES IMPORTS
+    , Install.Import.initSimple "Types" [ "Auth.Common", "MagicLink.Types", "User", "Session", "Dict", "AssocList" ] |> Install.Import.makeRule
+    , Install.Import.init "Types" [ { moduleToImport = "Url", alias_ = Nothing, exposedValues = Just [ "Url" ] } ] |> Install.Import.makeRule
+
+    -- Type Frontend, MagicLink
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "authFlow : Auth.Common.Flow"
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "authRedirectBaseUrl : Url"
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "signinForm : MagicLink.Types.SigninForm"
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "loginErrorMessage : Maybe String"
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "signInStatus : MagicLink.Types.SignInStatus"
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "currentUserData : Maybe User.LoginData"
+
+    -- Type Frontend, User
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "currentUser : Maybe User.User"
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "signInState : SignInState"
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "realname : String"
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "username : String"
+    , Install.FieldInTypeAlias.makeRule "Types" "FrontendModel" "email : String"
+
+    -- Type BackendModel
+    , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "pendingAuths : Dict Lamdera.SessionId Auth.Common.PendingAuth"
+    , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "pendingEmailAuths : Dict Lamdera.SessionId Auth.Common.PendingEmailAuth"
+    , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "sessions : Dict SessionId Auth.Common.UserInfo"
+    , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "secretCounter : Int"
+    , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "sessionDict : AssocList.Dict SessionId String"
+    , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "pendingLogins: MagicLink.Types.PendingLogins"
+    , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "log : MagicLink.Types.Log"
+    , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "users: Dict.Dict User.EmailString User.User"
+    , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "userNameToEmailString : Dict.Dict User.Username User.EmailString"
+    , Install.FieldInTypeAlias.makeRule "Types" "BackendModel" "sessionInfo : Session.SessionInfo"
+
+    -- Type ToBackend
+    , Install.TypeVariant.makeRule "Types" "ToBackend" "AuthToBackend Auth.Common.ToBackend"
+    , Install.TypeVariant.makeRule "Types" "ToBackend" "AddUser String String String"
+    , Install.TypeVariant.makeRule "Types" "ToBackend" "RequestSignup String String String"
+
+    -- Type BackendMsg
+    , Install.TypeVariant.makeRule "Types" "BackendMsg" "AuthBackendMsg Auth.Common.BackendMsg"
+    , Install.TypeVariant.makeRule "Types" "BackendMsg" "AutoLogin SessionId User.LoginData"
+
+    -- Type ToFrontend
+    , Install.TypeVariant.makeRule "Types" "ToFrontend" "AuthToFrontend Auth.Common.ToFrontend"
+    , Install.TypeVariant.makeRule "Types" "ToFrontend" "AuthSuccess Auth.Common.UserInfo"
+    , Install.TypeVariant.makeRule "Types" "ToFrontend" "UserInfoMsg (Maybe Auth.Common.UserInfo)"
+    , Install.TypeVariant.makeRule "Types" "ToFrontend" "CheckSignInResponse (Result BackendDataStatus User.LoginData)"
+    , Install.TypeVariant.makeRule "Types" "ToFrontend" "GetLoginTokenRateLimited"
+    , Install.TypeVariant.makeRule "Types" "ToFrontend" "RegistrationError String"
+    , Install.TypeVariant.makeRule "Types" "ToFrontend" "SignInError String"
+    , Install.TypeVariant.makeRule "Types" "ToFrontend" "UserSignedIn (Maybe User.User)"
+
+    -- Initialize BackendModel
+    , Install.Initializer.makeRule "Backend" "init" "users" "Dict.empty"
+    , Install.Initializer.makeRule "Backend" "init" "sessions" "Dict.empty"
+    , Install.Initializer.makeRule "Backend" "init" "time" "Time.millisToPosix 0"
+    , Install.Initializer.makeRule "Backend" "init" "time" "Time.millisToPosix 0"
+    , Install.Initializer.makeRule "Backend" "init" "randomAtmosphericNumbers" "Nothing"
+    , Install.Initializer.makeRule "Backend" "init" "localUuidData" "Dict.empty"
+    , Install.Initializer.makeRule "Backend" "init" "pendingAuths" "Nothing"
+    , Install.Initializer.makeRule "Backend" "init" "localUuidData" "Nothing"
+    , Install.Initializer.makeRule "Backend" "init" "secretCounter" "0"
+    , Install.Initializer.makeRule "Backend" "init" "pendingAuths" "Dict.empty"
+    , Install.Initializer.makeRule "Backend" "init" "pendingEmailAuths" "Dict.empty"
+    , Install.Initializer.makeRule "Backend" "init" "sessionDict" "AssocList.empty"
+    , Install.Initializer.makeRule "Backend" "init" "sessionDict" "AssocList.empty"
+    , Install.Initializer.makeRule "Backend" "init" "log" "[]"
+
+    -- Backend import
+    , Install.Import.initSimple "Backend"
+        [ "Auth.Common"
+        , "AssocList"
+        , "Auth.Flow"
+        , "Dict"
+        , "Helper"
+        , "LocalUUID"
+        , "MagicLink.Auth"
+        , "Process"
+        , "Task"
+        , "Time"
+        , "User"
+        ]
+        |> Install.Import.makeRule
+    , Install.Import.init "Backend" [ { moduleToImport = "Lamdera", alias_ = Nothing, exposedValues = Just [ "ClientId", "SessionId" ] } ] |> Install.Import.makeRule
+
+    ---
+    , Install.ClauseInCase.init
+        "Frontend"
+        "updateFromBacked"
+        "AuthToFrontend authToFrontendMsg"
+        "MagicLink.Auth.updateFromBackend authToFrontendMsg model"
+        |> Install.ClauseInCase.makeRule
     ]
 
-{-
 
 
-  updateFromBackendLoaded : ToFrontend -> LoadedModel -> ( LoadedModel, Cmd msg )
-  updateFromBackendLoaded msg model =
-      case msg of
-          AuthToFrontend authToFrontendMsg ->
-              MagicLink.Auth.updateFromBackend authToFrontendMsg model
+{-
 
-          GotBackendModel beModel ->
-              ( { model | backendModel = Just beModel }, Cmd.none )
 
-          -- MAGICLINK
-          AuthSuccess userInfo ->
-              -- TODO (placholder)
-              case userInfo.username of
-                  Just username ->
-                      ( { model | authFlow = Auth.Common.Authorized userInfo.email username }, Cmd.none )
+   updateFromBackendLoaded : ToFrontend -> LoadedModel -> ( LoadedModel, Cmd msg )
+   updateFromBackendLoaded msg model =
+       case msg of
+           AuthToFrontend authToFrontendMsg ->
+               MagicLink.Auth.updateFromBackend authToFrontendMsg model
 
-                  Nothing ->
-                      ( model, Cmd.none )
+           GotBackendModel beModel ->
+               ( { model | backendModel = Just beModel }, Cmd.none )
 
-          UserInfoMsg _ ->
-              -- TODO (placholder)
-              ( model, Cmd.none )
+           -- MAGICLINK
+           AuthSuccess userInfo ->
+               -- TODO (placholder)
+               case userInfo.username of
+                   Just username ->
+                       ( { model | authFlow = Auth.Common.Authorized userInfo.email username }, Cmd.none )
 
-          SignInError message ->
-              MagicLink.Frontend.handleSignInError model message
+                   Nothing ->
+                       ( model, Cmd.none )
 
-          RegistrationError str ->
-              MagicLink.Frontend.handleRegistrationError model str
+           UserInfoMsg _ ->
+               -- TODO (placholder)
+               ( model, Cmd.none )
 
-          CheckSignInResponse _ ->
-              ( model, Cmd.none )
+           SignInError message ->
+               MagicLink.Frontend.handleSignInError model message
 
-          GetLoginTokenRateLimited ->
-              ( model, Cmd.none )
+           RegistrationError str ->
+               MagicLink.Frontend.handleRegistrationError model str
 
-          UserRegistered user ->
-              MagicLink.Frontend.userRegistered model user
+           CheckSignInResponse _ ->
+               ( model, Cmd.none )
 
-          UserSignedIn maybeUser ->
-              ( { model | signInStatus = MagicLink.Types.NotSignedIn }, Cmd.none )
+           GetLoginTokenRateLimited ->
+               ( model, Cmd.none )
 
-          GotMessage message ->
-              ( { model | message = message }, Cmd.none )
+           UserRegistered user ->
+               MagicLink.Frontend.userRegistered model user
 
-          AdminInspectResponse backendModel ->
-              ( { model | backendModel = Just backendModel }, Cmd.none )
+           UserSignedIn maybeUser ->
+               ( { model | signInStatus = MagicLink.Types.NotSignedIn }, Cmd.none )
 
+           GotMessage message ->
+               ( { model | message = message }, Cmd.none )
 
-    , Cmd.batch
-        [ Time.now |> Task.perform GotFastTick
-        , Helper.getAtmosphericRandomNumbers
-        ]
-    )
--}
+           AdminInspectResponse backendModel ->
+               ( { model | backendModel = Just backendModel }, Cmd.none )
 
 
+     , Cmd.batch
+         [ Time.now |> Task.perform GotFastTick
+         , Helper.getAtmosphericRandomNumbers
+         ]
+     )
+-}
diff --git a/review/elm.json b/review/elm.json
index 364253d..7fd1552 100644
--- a/review/elm.json
+++ b/review/elm.json
@@ -9,7 +9,7 @@
             "elm/core": "1.0.5",
             "elm/json": "1.1.3",
             "elm/project-metadata-utils": "1.0.2",
-            "jfmengels/elm-review": "2.13.2",
+            "jfmengels/elm-review": "2.14.0",
             "jfmengels/elm-review-debug": "1.0.8",
             "jfmengels/elm-review-unused": "1.2.3",
             "jxxcarlson/elm-review-codeinstaller": "1.0.0",
@@ -20,11 +20,11 @@
             "elm/html": "1.0.0",
             "elm/parser": "1.1.0",
             "elm/random": "1.0.0",
+            "elm/regex": "1.0.0",
             "elm/time": "1.0.0",
             "elm/virtual-dom": "1.0.3",
             "elm-explorations/test": "2.2.0",
             "miniBill/elm-unicode": "1.1.1",
-            "pzp1997/assoc-list": "1.0.0",
             "rtfeldman/elm-hex": "1.0.0",
             "stil4m/structured-writer": "1.0.3"
         }
@@ -33,9 +33,6 @@
         "direct": {
             "elm-explorations/test": "2.2.0"
         },
-        "indirect": {
-            "elm/regex": "1.0.0",
-            "pzp1997/assoc-list": "1.0.0"
-        }
+        "indirect": {}
     }
 }
diff --git a/src/Install/Function.elm b/src/Install/Function/InsertFunction.elm
similarity index 53%
rename from src/Install/Function.elm
rename to src/Install/Function/InsertFunction.elm
index 3692c57..3f669ce 100644
--- a/src/Install/Function.elm
+++ b/src/Install/Function/InsertFunction.elm
@@ -1,45 +1,43 @@
-module Install.Function exposing (makeRule, init, Config, CustomError, withInsertAfter)
+module Install.Function.InsertFunction exposing (makeRule, init, Config, CustomError, withInsertAfter)
 
-{-| Replace a function in a given module with a new implementation or
-add that function definition if it is not present in the module.
+{-| Add a function in a given module if it is not present.
 
     -- code for ReviewConfig.elm:
     rule =
-        Install.Function.init
+        Install.Function.InsertFunction.init
             "Frontend"
             "view"
             """view model =
-       Html.text "This is a test\""""
-            |> Install.Function.makeRule
+            Html.text "This is a test\""""
+            |> Install.Function.InsertFunction.makeRule
+
+Running this rule will insert the function `view` in the module `Frontend` with the provided implementation.
 
-Running this rule will insert or replace the function `view` in the module `Frontend` with the new implementation.
 The form of the rule is the same for nested modules:
 
     rule =
-        Install.Function.init
+        Install.Function.InsertFunction.init
             "Foo.Bar"
             "earnInterest"
             "hoho model = { model | interest = 1.03 * model.interest }"
-            |> Install.Function.makeRule
+            |> Install.Function.InsertFunction.makeRule
 
 @docs makeRule, init, Config, CustomError, withInsertAfter
 
 -}
 
-import Elm.Syntax.Declaration exposing (Declaration(..))
-import Elm.Syntax.Expression exposing (Expression, Function)
+import Elm.Syntax.Declaration exposing (Declaration)
+import Elm.Syntax.Expression exposing (Expression)
 import Elm.Syntax.ModuleName exposing (ModuleName)
 import Elm.Syntax.Node as Node exposing (Node)
 import Elm.Syntax.Range as Range exposing (Range)
-import Install.Infer as Infer
 import Install.Library
-import Install.Normalize as Normalize
 import Review.Fix as Fix
 import Review.ModuleNameLookupTable exposing (ModuleNameLookupTable)
 import Review.Rule as Rule exposing (Error, Rule)
 
 
-{-| Configuration for makeRule: add (or replace if function already exists) a function in a specified module.
+{-| Configuration for makeRule: add a function in a specified module if it does not already exist.
 -}
 type Config
     = Config
@@ -79,13 +77,12 @@ init moduleNaeme functionName functionImplementation =
         , functionName = functionName
         , functionImplementation = functionImplementation
         , theFunctionNodeExpression = Install.Library.maybeNodeExpressionFromString { moduleName = String.split "." moduleNaeme } functionImplementation
-        , customErrorMessage = CustomError { message = "Replace function \"" ++ functionName ++ "\" with new code.", details = [ "" ] }
+        , customErrorMessage = CustomError { message = "Add function \"" ++ functionName ++ "\".", details = [ "" ] }
         , insertAt = AtEnd
         }
 
 
-{-| Create a rule that replaces a function in a given module with a new implementation or
-creates it if it is not present.
+{-| Create a rule that adds a function in a given module if it is not present.
 -}
 makeRule : Config -> Rule
 makeRule config =
@@ -94,7 +91,7 @@ makeRule config =
         visitor declaration context =
             declarationVisitor context config declaration
     in
-    Rule.newModuleRuleSchemaUsingContextCreator "Install.Function" initialContext
+    Rule.newModuleRuleSchemaUsingContextCreator "Install.Function.InsertFunction" initialContext
         |> Rule.withDeclarationEnterVisitor visitor
         |> Rule.withFinalModuleEvaluation (finalEvaluation config)
         |> Rule.providesFixesForModuleRule
@@ -120,10 +117,13 @@ initialContext =
 declarationVisitor : Context -> Config -> Node Declaration -> ( List (Rule.Error {}), Context )
 declarationVisitor context (Config config) declaration =
     let
+        declarationName =
+            Install.Library.getDeclarationName declaration
+
         contextWithLastDeclarationRange =
             case config.insertAt of
                 After previousDeclaration ->
-                    if getDeclarationName declaration == previousDeclaration then
+                    if Install.Library.getDeclarationName declaration == previousDeclaration then
                         { context | lastDeclarationRange = Node.range declaration }
 
                     else
@@ -132,49 +132,11 @@ declarationVisitor context (Config config) declaration =
                 AtEnd ->
                     { context | lastDeclarationRange = Node.range declaration }
     in
-    case Node.value declaration of
-        FunctionDeclaration function ->
-            let
-                name : String
-                name =
-                    getDeclarationName declaration
-
-                isInCorrectModule =
-                    Install.Library.isInCorrectModule config.moduleName context
-
-                resources =
-                    { lookupTable = context.lookupTable, inferredConstants = ( Infer.empty, [] ) }
-
-                -- isNotImplemented returns True if the values of the current function expression and the replacement expression are different
-                isNotImplemented : Function -> { a | functionImplementation : String } -> Bool
-                isNotImplemented f confg =
-                    Maybe.map2 (Normalize.compare resources)
-                        (f.declaration |> Node.value |> .expression |> Just)
-                        (Install.Library.getExpressionFromString context confg.functionImplementation)
-                        == Just Normalize.ConfirmedEquality
-                        |> not
-
-                isImplemented =
-                    not (isNotImplemented function config)
-            in
-            if isImplemented then
-                ( [], { contextWithLastDeclarationRange | appliedFix = True } )
-
-            else if name == config.functionName && isInCorrectModule && isNotImplemented function config then
-                replaceFunction { range = Node.range declaration, functionName = config.functionName, functionImplementation = config.functionImplementation } context
-
-            else
-                ( [], contextWithLastDeclarationRange )
+    if declarationName == config.functionName then
+        ( [], { context | appliedFix = True } )
 
-        _ ->
-            ( [], contextWithLastDeclarationRange )
-
-
-type alias FixConfig =
-    { range : Range
-    , functionName : String
-    , functionImplementation : String
-    }
+    else
+        ( [], contextWithLastDeclarationRange )
 
 
 finalEvaluation : Config -> Context -> List (Rule.Error {})
@@ -186,15 +148,11 @@ finalEvaluation (Config config) context =
         []
 
 
-replaceFunction : FixConfig -> Context -> ( List (Error {}), Context )
-replaceFunction fixConfig context =
-    ( [ Rule.errorWithFix
-            { message = "Replace function \"" ++ fixConfig.functionName ++ "\"", details = [ "" ] }
-            fixConfig.range
-            [ Fix.replaceRangeBy fixConfig.range fixConfig.functionImplementation ]
-      ]
-    , { context | appliedFix = True }
-    )
+type alias FixConfig =
+    { range : Range
+    , functionName : String
+    , functionImplementation : String
+    }
 
 
 addFunction : FixConfig -> List (Error {})
@@ -204,26 +162,3 @@ addFunction fixConfig =
         fixConfig.range
         [ Fix.insertAt { row = fixConfig.range.end.row + 1, column = 0 } fixConfig.functionImplementation ]
     ]
-
-
-getDeclarationName : Node Declaration -> String
-getDeclarationName declaration =
-    let
-        getName declaration_ =
-            declaration_ |> .name >> Node.value
-    in
-    case Node.value declaration of
-        FunctionDeclaration function ->
-            getName (Node.value function.declaration)
-
-        AliasDeclaration alias_ ->
-            getName alias_
-
-        CustomTypeDeclaration customType ->
-            getName customType
-
-        PortDeclaration port_ ->
-            getName port_
-
-        _ ->
-            ""
diff --git a/src/Install/Function/ReplaceFunction.elm b/src/Install/Function/ReplaceFunction.elm
new file mode 100644
index 0000000..c7087e2
--- /dev/null
+++ b/src/Install/Function/ReplaceFunction.elm
@@ -0,0 +1,155 @@
+module Install.Function.ReplaceFunction exposing (makeRule, init, Config, CustomError)
+
+{-| Replace a function in a given module with a new implementation.
+
+    -- code for ReviewConfig.elm:
+    rule =
+        Install.Function.InsertFunction.init
+            "Frontend"
+            "view"
+            """view model =
+            Html.text "This is a test\""""
+            |> Install.Function.InsertFunction.makeRule
+
+Running this rule will replace the function `view` in the module `Frontend` with the provided implementation.
+
+The form of the rule is the same for nested modules:
+
+    rule =
+        Install.Function.ReplaceFunction.init
+            "Foo.Bar"
+            "earnInterest"
+            "hoho model = { model | interest = 1.03 * model.interest }"
+            |> Install.Function.ReplaceFunction.makeRule
+
+@docs makeRule, init, Config, CustomError
+
+-}
+
+import Elm.Syntax.Declaration exposing (Declaration(..))
+import Elm.Syntax.Expression exposing (Expression, Function)
+import Elm.Syntax.ModuleName exposing (ModuleName)
+import Elm.Syntax.Node as Node exposing (Node)
+import Elm.Syntax.Range exposing (Range)
+import Install.Infer as Infer
+import Install.Library
+import Install.Normalize as Normalize
+import Review.Fix as Fix
+import Review.ModuleNameLookupTable exposing (ModuleNameLookupTable)
+import Review.Rule as Rule exposing (Error, Rule)
+
+
+{-| Configuration for makeRule: replace a function in a specified module with a new implementation.
+-}
+type Config
+    = Config
+        { moduleName : String
+        , functionName : String
+        , functionImplementation : String
+        , theFunctionNodeExpression : Maybe (Node Expression)
+        , customErrorMessage : CustomError
+        }
+
+
+{-| Custom error message to be displayed when running `elm-review --fix` or `elm-review --fix-all`
+-}
+type CustomError
+    = CustomError { message : String, details : List String }
+
+
+{-| Initialize the configuration for the rule.
+-}
+init : String -> String -> String -> Config
+init moduleNaeme functionName functionImplementation =
+    Config
+        { moduleName = moduleNaeme
+        , functionName = functionName
+        , functionImplementation = functionImplementation
+        , theFunctionNodeExpression = Install.Library.maybeNodeExpressionFromString { moduleName = String.split "." moduleNaeme } functionImplementation
+        , customErrorMessage = CustomError { message = "Replace function \"" ++ functionName ++ "\" with new code.", details = [ "" ] }
+        }
+
+
+{-| Create a rule that replaces a function in a given module with a new implementation.
+-}
+makeRule : Config -> Rule
+makeRule config =
+    let
+        visitor : Node Declaration -> Context -> ( List (Error {}), Context )
+        visitor declaration context =
+            declarationVisitor context config declaration
+    in
+    Rule.newModuleRuleSchemaUsingContextCreator "Install.Function.ReplaceFunction" initialContext
+        |> Rule.withDeclarationEnterVisitor visitor
+        |> Rule.providesFixesForModuleRule
+        |> Rule.fromModuleRuleSchema
+
+
+type alias Context =
+    { moduleName : ModuleName
+    , lookupTable : ModuleNameLookupTable
+    }
+
+
+initialContext : Rule.ContextCreator () Context
+initialContext =
+    Rule.initContextCreator
+        (\lookupTable moduleName () -> { lookupTable = lookupTable, moduleName = moduleName })
+        |> Rule.withModuleNameLookupTable
+        |> Rule.withModuleName
+
+
+declarationVisitor : Context -> Config -> Node Declaration -> ( List (Rule.Error {}), Context )
+declarationVisitor context (Config config) declaration =
+    case Node.value declaration of
+        FunctionDeclaration function ->
+            let
+                name : String
+                name =
+                    Install.Library.getDeclarationName declaration
+
+                isInCorrectModule =
+                    Install.Library.isInCorrectModule config.moduleName context
+
+                resources =
+                    { lookupTable = context.lookupTable, inferredConstants = ( Infer.empty, [] ) }
+
+                isInCorrectFunction =
+                    isInCorrectModule && name == config.functionName
+
+                isNotImplemented : Function -> { a | functionImplementation : String } -> Bool
+                isNotImplemented f confg =
+                    isInCorrectFunction
+                        && (Maybe.map2 (Normalize.compare resources)
+                                (f.declaration |> Node.value |> .expression |> Just)
+                                (Install.Library.getExpressionFromString context confg.functionImplementation)
+                                == Just Normalize.ConfirmedEquality
+                                |> not
+                           )
+            in
+            if isNotImplemented function config then
+                replaceFunction { range = Node.range declaration, functionName = config.functionName, functionImplementation = config.functionImplementation } context
+
+            else
+                ( [], context )
+
+        _ ->
+            ( [], context )
+
+
+replaceFunction : FixConfig -> Context -> ( List (Error {}), Context )
+replaceFunction fixConfig context =
+    ( [ Rule.errorWithFix
+            { message = "Replace function \"" ++ fixConfig.functionName ++ "\"", details = [ "" ] }
+            fixConfig.range
+            [ Fix.replaceRangeBy fixConfig.range fixConfig.functionImplementation ]
+      ]
+    , context
+    )
+
+
+type alias FixConfig =
+    { range : Range
+    , functionName : String
+    , functionImplementation : String
+    }
diff --git a/src/Install/Library.elm b/src/Install/Library.elm
index 8878dcd..d5ac5d6 100644
--- a/src/Install/Library.elm
+++ b/src/Install/Library.elm
@@ -254,3 +254,26 @@ isInCorrectModule moduleName context =
     context.moduleName
         |> String.join "."
         |> (==) moduleName
+
+
+getDeclarationName : Node Declaration -> String
+getDeclarationName declaration =
+    let
+        getName declaration_ =
+            declaration_ |> .name >> Node.value
+    in
+    case Node.value declaration of
+        FunctionDeclaration function ->
+            getName (Node.value function.declaration)
+
+        AliasDeclaration alias_ ->
+            getName alias_
+
+        CustomTypeDeclaration customType ->
+            getName customType
+
+        PortDeclaration port_ ->
+            getName port_
+
+        _ ->
+            ""
diff --git a/tests/Install/FunctionTest.elm b/tests/Install/FunctionTest.elm
index a48a61d..5707981 100644
--- a/tests/Install/FunctionTest.elm
+++ b/tests/Install/FunctionTest.elm
@@ -1,6 +1,7 @@
 module Install.FunctionTest exposing (all)
 
-import Install.Function
+import Install.Function.InsertFunction as InsertFunction
+import Install.Function.ReplaceFunction as ReplaceFunction
 import Review.Rule exposing (Rule)
 import Run
 import Test exposing (Test, describe)
@@ -36,12 +37,12 @@ test1 =
 
 rule1 : Rule
 rule1 =
-    Install.Function.init
+    ReplaceFunction.init
         "Frontend"
         "view"
         """view model =
     Html.text "This is a test\""""
-        |> Install.Function.makeRule
+        |> ReplaceFunction.makeRule
 
 
 src1 : String
@@ -103,12 +104,12 @@ test2 =
 
 rule2 : Rule
 rule2 =
-    Install.Function.init
+    InsertFunction.init
         "Frontend"
         "newFunction"
         """newFunction model =
     Html.text "This is a test\""""
-        |> Install.Function.makeRule
+        |> InsertFunction.makeRule
 
 
 under2 : String
@@ -168,12 +169,12 @@ type alias Model =
 
 rule3 : Rule
 rule3 =
-    Install.Function.init
+    InsertFunction.init
         "Frontend"
         "newFunction"
         """newFunction model =
     Html.text "This is a test\""""
-        |> Install.Function.makeRule
+        |> InsertFunction.makeRule
 
 
 under3 : String
@@ -212,13 +213,13 @@ test4 =
 
 rule4 : Rule
 rule4 =
-    Install.Function.init
+    InsertFunction.init
         "Frontend"
         "newFunction"
         """newFunction model =
     Html.text "This is a test\""""
-        |> Install.Function.withInsertAfter "view"
-        |> Install.Function.makeRule
+        |> InsertFunction.withInsertAfter "view"
+        |> InsertFunction.makeRule
 
 
 under4 : String
@@ -259,13 +260,13 @@ test4a =
 
 rule4a : Rule
 rule4a =
-    Install.Function.init
+    InsertFunction.init
         "Frontend"
         "newFunction"
         """newFunction model =
     Html.text "This is a test\""""
-        |> Install.Function.withInsertAfter "Model"
-        |> Install.Function.makeRule
+        |> InsertFunction.withInsertAfter "Model"
+        |> InsertFunction.makeRule
 
 
 under4a : String
@@ -305,13 +306,13 @@ test4b =
 
 rule4b : Rule
 rule4b =
-    Install.Function.init
+    InsertFunction.init
         "Frontend"
         "newFunction"
         """newFunction model =
     Html.text "This is a test\""""
-        |> Install.Function.withInsertAfter "Model"
-        |> Install.Function.makeRule
+        |> InsertFunction.withInsertAfter "Model"
+        |> InsertFunction.makeRule
 
 
 under4b : String