kotlin applicative example

validation.kt

package com.yanbin.fpworkshop.part4

import arrow.core.Try
import arrow.core.Tuple2
import arrow.core.flatten
import java.time.LocalDate

interface Validation {
    fun validateAccountNo(no: String): Try<String>
    fun validateAccountName(name: String): Try<String>
    fun validateOpenDate(date: LocalDate): Try<LocalDate>
}

fun createAccount(validation: Validation, no: String, name: String, date: LocalDate): Try<Account> {
    return validation.validateAccountNo(no).flatMap { vNo ->
        validation.validateAccountName(name).flatMap { vName ->
            validation.validateOpenDate(date).flatMap { vDate ->
                AccountService.open(vNo, vName, vDate)
            }
        }
    }
}

fun createAccountAp(validation: Validation, no: String, name: String, date: LocalDate): Try<Account> {
    val openFun = { no:String -> {name:String -> {date: LocalDate -> AccountService.open(no, name, date)}} }

    val openAp = validation.validateAccountNo(no).map { openFun(it) }

    val openAp2 = validation.validateAccountName(name).ap(openAp)

    val openAp3 = validation.validateOpenDate(date).ap(openAp2).flatten()

    return openAp3
}

fun main(args: Array<String>) {
    val application = AccountApplication()
    val account1 = Account("1", "Eric", Balance(400))
    val account2 = Account("2", "John", Balance(100))

    val transferResult = application.transferAp(account1, account2, 500)
    println(transferResult)
}