Create TimerOpResult for reporting of results related to timers

replace RemoveTimerResult with this

this will also be used for pause/resume timer

src/Sand/Basic.lean

@@ -94,10 +94,8 @@ inductive Command
 
 -- responses to commands sent from server to client
 inductive CmdResponse
- -- acknowledgement of `addTimer` and `cancelTimer`
  | ok
  | list (timers : Array Timer)
- -- response to `cancelTimer` of nonexistent `TimerId`
  | timerNotFound (which : TimerId)
  deriving ToJson, FromJson
 

src/Sand/SandDaemon.lean

@@ -29,19 +29,20 @@ def addTimer (state : SanddState) (due : Nat) : BaseIO TimerId := do
  state.timers.atomically <| modify (·.insert id timer)
  return id
 
-inductive RemoveTimerResult
- | removed
+inductive TimerOpError
  | notFound
 
-def removeTimer (state : SanddState) (id : TimerId) : BaseIO RemoveTimerResult := do
+def TimerOpResult α := Except TimerOpError α
+
+def removeTimer (state : SanddState) (id : TimerId) : BaseIO (TimerOpResult Unit) := do
  let timers ← state.timers.atomically get
  -- match timers.findIdx? (λ timer ↦ timer.id == id) with
  match timers.find? id with
  | some _ => do
  state.timers.atomically <| set <| timers.erase id
- pure .removed
+ pure <| .ok ()
  | none => do
- pure .notFound
+ pure <| .error .notFound
 
 def timerExists (state : SanddState) (id : TimerId) : BaseIO Bool := do
  let timers ← state.timers.atomically get
@@ -120,9 +121,9 @@ def handleClientCmd
  _ ← client.send CmdResponse.ok.serialize
  | .cancelTimer which => do
  match ← state.removeTimer which with
- | .notFound => do
+ | .error .notFound => do
  _ ← client.send <| (CmdResponse.timerNotFound which).serialize
- | .removed => do
+ | .ok () => do
  _ ← client.send CmdResponse.ok.serialize
  | .list => do
  let timers ← state.timers.atomically get