effmodel

EffModel embodies a single value that carries both the model and accumulated effects for a world step in the elm architecture.

The elm architecture is nice, but a tuple of model and effect is troublesome to compose. Consider the standard update function:

update : Action -> Model -> (Model, Effects Action)

In order to compose it, you need to destructure the result, use Effects.batch on the snd, and map on the first, then combine a new tuple. EffModel replaces this process and has functions that construct an effmodel either from a model or an update result tuple, and that produce an update result tuple from an EffModel.

I use it extensively like this:

import EffModel as EF

handleUpdateForOneLogicalThing : Action -> EffModel Model Action -> EffModel Model Action
handleUpdateForOneLogicalThing action effmodel =
    case action of
        Increment -> effmodel |> EF.map (\m -> { m | count = m.count + 1 })
        Decrement ->
            effmodel
                -- Compose model update and an effect conveniently
                |> EF.map (\m -> { m | count = m.count - 1 })
                |> EF.eff (Effects.task (Task.sleep (5 * Time.second) `Task.andThen` (\_ -> Task.succeed Increment)))
        _ -> effmodel -- Note that you can just pass it through easily

handleUpdateForAnotherLogicalThing : Action -> EffModel Model Action -> EffModel Model Action

update : Action -> Model -> (Model, Effects Action)
update action model =
    model
       |> wrap
       |> handleUpdateForOneLogicalThing action
       |> handleUpdateForAnotherLogicalThing action
       |> unwrap