The React framework for Haskell.

import Miso
  ( Component, Effect, View, component
  , vfrag, text, startApp, defaultEvents
  )
import Miso.Lens (this, (+=), (-=))
import Miso.String (ms)
import Miso.Html.Element (button_)
import Miso.Html.Event (onClick)

data Action = Add | Subtract

counter
  :: Component context props Int Action
counter = component m u v
  where
    m :: Int
    m = 0

    u :: Action
      -> Effect context props Int Action
    u = \case
      Add      -> this += 1
      Subtract -> this -= 1

    v :: context
      -> props
      -> Int
      -> View context Int Action
    v _ _ n = vfrag
      [ button_ [ onClick Subtract ] [ "−" ]
      , text (ms n)
      , button_ [ onClick Add ] [ "+" ]
      ]

main :: IO ()
main = startApp defaultEvents counter