foldp.js

// foldp : (a -> state -> state) -> state -> Signal a -> Signal b
var foldp = (updateFunction) => (defaultState) => (signal) =>
  updateFunction(defaultState)(signal)

const INCREMENT = 'INCREMENT'
const DECREMENT = 'DECREMENT'

const Actions = {
  increment: () => ({ type: INCREMENT }),
  decrement: () => ({ type: DECREMENT })
}

// update : Model -> Action -> Model
const update = (state) => (action) => {
  switch (action.type) {
    case INCREMENT:
      return state + 1
      break;
    case DECREMENT:
      return state + 1
      break;
    default:
      return state
  }
}

var state = foldp(update)(5)(Actions.increment())

console.log("state", state);