016-railway.ts

const { compose, curry } = require('lodash/fp')

// Success :: a -> Success a
const Success = value => ({
  type: 'success',
  value
})

Success.is = obj => obj.type === 'success'

// Failure :: a -> Failure a
const Failure = value => ({
  type: 'failure',
  value
})

Failure.is = (obj) => obj.type === 'failure'

// validateUserName :: User -> Success User | Failure
const validateUserName = user => {
  return !user.name
    ? Failure("Name is required")
    : Success(user)
}

// validateUserAge :: User -> Success User | Failure
const validateAge = user => {
  return user.age < 18
    ? Failure("User is underage")
    : Success(user)
}

// bind :: (Success a -> Success a | Failure ) -> Success a -> Succes a | Failure
const bind = curry((fn, data) => {
  if (Success.is(data)) {
    return fn(data.value)
  }
  
  if (Failure.is(data)) {
    return data
  }
});

const john = {
  name: "john doe",
  age: 18
}

// incrementAge :: User -> User
const incrementAge = user => {
  return {
    ...user,
    age: user.age + 1
  }
}

// map :: (a -> b) -> a -> Success a | Failure
const map = curry((fn, data) => {
  if (Success.is(data)) {
    return Success(fn(data.value))
  }

  if (Failure.is(data)) {
    return data
  }
})

// tee :: (a -> b) -> a -> a
const tee = curry((fn, data) => {
  fn(data)
  return data
})

// log :: a -> ()
const log = msg => {
  console.log(msg)
}

// canDrinkAlcohol :: User -> User
const canDrinkAlcohol = user => {
  if (user.age < 21) {
    throw new Error("Cannot drink, is underage")
  }

  return user
}

// tryCatch :: (a -> b) -> Success a -> Success b | Failure
const tryCatch = curry((fn, data) => {
  try {
    return Success(fn(data.value))
  } catch(err) {
    return Failure(err.message)
  }
})

// fold :: (a -> ()) -> (b -> ()) -> Success a | Failure -> ()
const fold = curry((success, failure, data) => {
  if (Failure.is(data)) {
    failure(data.value)
  }

  if (Success.is(data)) {
    success(data.value)
  }
})

const notifySuccess = data => {
  console.log("success: ", data, " yay!")
}

const notifyFailure = msg => {
  console.log("failure:", data, " nay!")
}

// validateUser :: User -> Success User | Failure string
const validateUser = compose(
  fold(notifySuccess, notifyFailure),
  tryCatch(canDrinkAlcohol),
  map(incrementAge),
  map(incrementAge),
  map(incrementAge),
  bind(validateAge),
  validateUserName
)

validateUser(john)