Add Light example

samples/Store/Domain.Tests/Domain.Tests.fsproj

@@ -10,6 +10,7 @@
     <Compile Include="ContactPreferencesTests.fs" />
     <Compile Include="FavoritesTests.fs" />
     <Compile Include="SavedForLaterTests.fs" />
+    <Compile Include="LightTests.fs" />
   </ItemGroup>
 
   <ItemGroup>

samples/Store/Domain.Tests/LightTests.fs

@@ -0,0 +1,27 @@
+module Domain.Tests.LightTests
+
+open Domain.Light
+open Swensen.Unquote
+
+type Cases = Off | On | After3Cycles
+let establish = function
+    | Off ->          initial
+    | On ->           fold initial [| SwitchedOn |]
+    | After3Cycles -> [| for _ in 1..3 do SwitchedOn; SwitchedOff |] |> fold initial
+
+let run cmd state =
+    let events = decideSwitch cmd state
+    events, fold state events
+
+let [<FsCheck.Xunit.Property>] props case cmd =
+    let state = establish case
+    let events, state = run cmd state
+    match case, cmd with
+    | Off,          true ->  events =! [| SwitchedOn |]
+    | Off,          false -> events =! [||]
+    | On,           true ->  events =! [||]
+    | On,           false -> events =! [| SwitchedOff |]
+    | After3Cycles, true ->  events =! [| Broke |]
+    | After3Cycles, false -> events =! [||]
+
+    [||] = decideSwitch cmd state // all commands are idempotent

samples/Store/Domain/Light.fs

@@ -2,42 +2,33 @@ module Domain.Light
 
 // By Jérémie Chassaing / @thinkb4coding
 // https://github.com/dddeu/dddeu20-talks-jeremie-chassaing-functional-event-sourcing/blob/main/EventSourcing.fsx#L52-L84
-type Command =
 
-    | SwitchOn
-    | SwitchOff
 type Event =
     | SwitchedOn
     | SwitchedOff
     | Broke
-
-type Status =
-    | On
-    | Off
-
-type Working =
-    { Status : Status
-      RemainingUses: int}
-
 type State =
-    | Working of Working
+    | Working of CurrentState
     | Broken
-let initialState = Working { Status = Off; RemainingUses = 3}
-
-let decide (command: Command) (state: State) : Event list =
-    match state, command with
-    | Working { Status = Off; RemainingUses = 0 }, SwitchOn ->
-        [ Broke]
-    | Working { Status = Off}, SwitchOn -> [ SwitchedOn]
-    |  Working { Status = On }, SwitchOff -> [SwitchedOff]
-    | _ -> []
+and CurrentState = { on: bool; remainingUses: int }
+let initial = Working { on = false; remainingUses = 3 }
+let evolve s e =
+    match s with
+    | Broken -> s
+    | Working s ->
+        match e with
+        | SwitchedOn -> Working { on = true; remainingUses = s.remainingUses - 1 }
+        | SwitchedOff -> Working { s with on = false }
+        | Broke -> Broken
+let fold = Array.fold evolve
 
-let evolve (state: State) (event: Event) : State =
-    match state, event with
-    | _, Broke -> Broken
-    | Working s, SwitchedOn ->
-        Working { Status = On;
-                  RemainingUses = s.RemainingUses - 1 }
-    | Working s, SwitchedOff ->
-        Working { s with Status = Off}
-    | _ -> state
+let decideSwitch (on: bool) s = [|
+    match s with
+    | Broken -> ()
+    | Working { on = true } ->
+        if not on then
+            SwitchedOff
+    | Working { on = false; remainingUses = r } ->
+        if on then
+            if r = 0 then Broke
+            else SwitchedOn |]