Expand state shim to inform if function application changed app state

Some projects use this information to decide whether to persist the originating event. One example is rate-limiting in a web server application: When a client floods the server with HTTP requests when the server rejects 99% of them because of a rate-limiting scheme, it may be better not to persist these events in the event log.
pine-vm · Mar 25, 2023 · 8cb642d · 8cb642d
1 parent dfc138b
commit 8cb642d
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Showing 4 changed files with 17 additions and 5 deletions.
diff --git a/implement/elm-time/ElmTime/StateShim/InterfaceToHost/InterfaceToHost.cs b/implement/elm-time/ElmTime/StateShim/InterfaceToHost/InterfaceToHost.cs
@@ -88,7 +88,9 @@ public record JsonStateSource(JsonElement Json) : StateSource;
     public record BranchStateSource(string Branch) : StateSource;
 }
 
-public record FunctionApplicationResult(Maybe<JsonElement> resultLessStateJson);
+public record FunctionApplicationResult(
+    Maybe<JsonElement> resultLessStateJson,
+    bool producedStateDifferentFromStateArgument);
 
 public record NamedExposedFunction(string functionName, ExposedFunctionDescription functionDescription);
 

diff --git a/implement/elm-time/ElmTime/compile-elm-program/src/CompileElmAppWithStateShim.elm b/implement/elm-time/ElmTime/compile-elm-program/src/CompileElmAppWithStateShim.elm
@@ -626,6 +626,10 @@ processEvent config hostEvent stateBefore =
 
                                 Ok ( maybeFunctionResultState, maybeFunctionResultOther ) ->
                                     let
+                                        producedStateDifferentFromStateArgument =
+                                            (maybeFunctionResultState /= Nothing)
+                                                && (maybeFunctionResultState /= stateArgument)
+
                                         updateStateResult =
                                             case applyFunction.stateDestinationBranches of
                                                 [] ->
@@ -647,7 +651,12 @@ processEvent config hostEvent stateBefore =
 
                                         Ok state ->
                                             ( state
-                                            , ApplyFunctionShimResponse (Ok { resultLessStateJson = maybeFunctionResultOther })
+                                            , ApplyFunctionShimResponse
+                                                (Ok
+                                                    { resultLessStateJson = maybeFunctionResultOther
+                                                    , producedStateDifferentFromStateArgument = producedStateDifferentFromStateArgument
+                                                    }
+                                                )
                                             )
 
         SerializeStateShimRequest stateSource ->
@@ -861,6 +870,7 @@ type alias ExposedFunctionDescription =
 
 type alias FunctionApplicationResult =
     { resultLessStateJson : Maybe Json.Encode.Value
+    , producedStateDifferentFromStateArgument : Bool
     }
 
 """
diff --git a/implement/elm-time/Program.cs b/implement/elm-time/Program.cs
@@ -16,7 +16,7 @@ namespace ElmTime;
 
 public class Program
 {
-    static public string AppVersionId => "2023-03-24";
+    static public string AppVersionId => "2023-03-25";
 
     static int AdminInterfaceDefaultPort => 4000;
 

diff --git a/implement/elm-time/elm-time.csproj b/implement/elm-time/elm-time.csproj
@@ -5,8 +5,8 @@
     <TargetFramework>net7.0</TargetFramework>
     <RootNamespace>ElmTime</RootNamespace>
     <AssemblyName>elm-time</AssemblyName>
-    <AssemblyVersion>2023.0324.0.0</AssemblyVersion>
-    <FileVersion>2023.0324.0.0</FileVersion>
+    <AssemblyVersion>2023.0325.0.0</AssemblyVersion>
+    <FileVersion>2023.0325.0.0</FileVersion>
     <Nullable>enable</Nullable>
     <GenerateEmbeddedFilesManifest>true</GenerateEmbeddedFilesManifest>
   </PropertyGroup>