Executing Logic

Workflows4s supports two ways of embedding custom logic within a workflow:

1. Deterministic (Pure) Operations - operations that always produce the same output for the same input, without any side effects
2. Nondeterministic Operations - operations that may produce different outputs for the same input, typically involving side effects

Deterministic operations are executed with each workflow recovery, while nondeterministic ones are memoized through event persistance.

Deterministic (Pure) Operations

Without Error

val doThings: WIO[Any, Nothing, MyState] =
  WIO.pure(MyState(1)).autoNamed

val doThings2: WIO[MyState, Nothing, MyState] =
  WIO.pure
    .makeFrom[MyState]
    .value(state => MyState(state.counter))
    .autoNamed

Rendering Outputs

Flowchart

BPMN

Model

{
  "meta" : {
    "name" : "Do Things",
    "error" : null
  },
  "_type" : "Pure"
}

With Error

val doThingsWithError: WIO[Any, MyError, Nothing] =
  WIO.pure.error(MyError()).autoNamed

val doThingsWithError2: WIO[MyState, MyError, Nothing] =
  WIO.pure
    .makeFrom[MyState]
    .error(_ => MyError())
    .autoNamed

Rendering Outputs

Flowchart

BPMN

Model

{
  "meta" : {
    "name" : "Do Things With Error",
    "error" : {
      "name" : "My Error"
    }
  },
  "_type" : "Pure"
}

note

Unnamed pure elements are considered technical in nature and are not rendered in diagrams. To make them visible, use .named("Name") or .autoNamed.

Nondeterministic Operations (Side Effects)

Nondeterministic operations involve side effects like API calls, database operations, or other external interactions. These operations need special handling because they shouldn't be re-executed during workflow recovery.

info

Workflows4s currently supports onyl cats-effect IO. If you're interested in other effect systems, please check here.

Without Error

val doThings: WIO[MyState, Nothing, MyState] =
  WIO
    .runIO[MyState](state => IO(MyEvent()))
    .handleEvent((state, event) => MyState(state.counter + 1))
    .autoNamed

Rendering Outputs

Flowchart

BPMN

Model

{
  "meta" : {
    "name" : "Do Things",
    "error" : null
  },
  "_type" : "RunIO"
}

With Error

val doThingsWithError: WIO[MyState, MyError, MyState] =
  WIO
    .runIO[MyState](state => IO(MyEvent()))
    .handleEventWithError((state, event) =>
      if (true) MyState(state.counter + 1).asRight
      else MyError().asLeft,
    )
    .autoNamed

Rendering Outputs

Flowchart

BPMN

Model

{
  "meta" : {
    "name" : "Do Things With Error",
    "error" : {
      "name" : "My Error"
    }
  },
  "_type" : "RunIO"
}

note

Errors render in flowchart only when they are handled