Overview

Miso.State re-exports the RWS combinators that are most useful inside an Effect handler. Because Effect is an RWS monad, the full MonadState, MonadReader, and MonadWriter interfaces are available without importing mtl directly.

This module is re-exported in its entirety by Miso, so most applications do not need to import it explicitly.

Quick start

import Miso          -- re-exports Miso.State
-- or
import Miso.State    -- explicit import

data Model = Model { _count :: Int } deriving (Eq)
data Action = Increment | Decrement | Reset | Log

update :: Action -> Effect p props Model Action
update Increment = modify (\m -> m { _count = _count m + 1 })
update Decrement = modify' (\m -> m { _count = _count m - 1 })
update Reset     = put (Model 0)
update Log       = do
  n <- gets _count
  io_ (consoleLog (ms n))

When using Miso.Lens or Miso.Lens.TH, the lens update operators (.=, +=, %=, …) are built directly on modify, so explicit calls to modify / put are rarely needed.

Exported combinators

• Reader (component metadata): ask, asks
• State (model): get, gets, modify, modify', put
• Writer (schedule IO): tell
• IO lift: liftIO

See also

• Miso.Effect — Effect, io, io_, sync
• Miso.Lens — lens operators that wrap modify
• Miso.Lens.TH — Template Haskell lens generation