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@pjambet
Last active Jul 15, 2020
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ROP Scala Parallel Validation
object Railway {
sealed trait TwoTrack[F]
case class Success[S](data: S) extends TwoTrack[S]
case class Failure[S](message: String) extends TwoTrack[S]
def succeed[S](x: S) = Success(x)
def fail[S](message: String) = Failure[S](message)
def bind[A, B](switchFunction: A => TwoTrack[B]): TwoTrack[A] => TwoTrack[B] = {
{ (twoTrackInput: TwoTrack[A]) =>
twoTrackInput match {
case Success(s) => switchFunction(s)
case Failure(f) => fail(f)
}
}
}
def map[A, B](singleTrackFunction: A => B): TwoTrack[A] => TwoTrack[B] = { twoTrackInput: TwoTrack[A] =>
twoTrackInput match {
case Success(s) => succeed(singleTrackFunction(s))
case Failure(f) => fail(f)
}
}
def map2[A, B](singleTrackFunction: A => B): TwoTrack[A] => TwoTrack[B] = {
bind(singleTrackFunction.andThen(succeed))
}
def tee[A](deadEndFunction: A => Unit)(a: A): A = {
deadEndFunction(a)
a
}
def tryCatch[A, B](f: A => B)(exnHandler: Throwable => String)(x: A): TwoTrack[B] = try {
succeed(f(x))
} catch {
case ex: Throwable =>
fail(exnHandler(ex))
}
def doubleMap[A, B](successFunc: A => B)
(failureFunc: String => String)
(twoTrackInput: TwoTrack[A]): TwoTrack[B] = twoTrackInput match {
case Success(s) => succeed(successFunc(s))
case Failure(f) => fail(failureFunc(f))
}
def log[A](twoTrackInput: TwoTrack[A]): TwoTrack[A] = {
val success = { x: A => println(s"DEBUG. Success so far: $x"); x }
val failure = { x: String => println(s"ERROR. $x"); x }
doubleMap(success)(failure)(twoTrackInput)
}
def plus[A, B](addSuccess: (B, B) => B,
addFailure: (String, String) => String,
switch1: A => TwoTrack[B],
switch2: A => TwoTrack[B])
(x: A): TwoTrack[B] = {
(switch1(x), switch2(x)) match {
case (Success(s1), Success(s2)) => Success(addSuccess(s1, s2))
case (Failure(f1), Success(_)) => Failure(f1)
case (Success(_), Failure(f2)) => Failure(f2)
case (Failure(f1), Failure(f2)) => Failure(addFailure(f1, f2))
}
}
// ---
case class Request(name: String, email: String)
def nameNotBlank: Request => TwoTrack[Request] = { request: Request =>
if (request.name == "") {
fail("Name must not be blank")
} else {
succeed(request)
}
}
def name50: Request => TwoTrack[Request] = { request: Request =>
if (request.name.length > 50) {
fail("Name must not be longer than 50 chars")
} else {
succeed(request)
}
}
def emailNotBlank: Request => TwoTrack[Request] = { request: Request =>
if (request.email == "") {
fail("Email must not be blank")
} else {
succeed(request)
}
}
sealed case class ComposableSwitch[A, B](v1: A => TwoTrack[B]) {
def &&&(v2: A => TwoTrack[B]): A => TwoTrack[B] = {
val addSuccess: (B, B) => B = (r1: B, _: B) => r1
val addFailure: (String, String) => String = (s1: String, s2: String) => s"$s1; $s2"
plus(addSuccess, addFailure, v1, v2)
}
}
implicit def functionToComposableFunction[A, B](f: A => TwoTrack[B]) = ComposableSwitch(f)
def validateRequest: Request => TwoTrack[Request] =
nameNotBlank &&& name50 &&& emailNotBlank
def validateRequest_inlined(input: Request): TwoTrack[Request] = {
val nameNotBlankResult = if (input.name == "") {
fail("Name must not be blank")
} else {
succeed(input)
}
nameNotBlankResult match {
case Success(s) => {
val name50Result = if (s.name.length > 50) {
fail("Name must not be longer than 50 chars")
} else {
succeed(s)
}
name50Result match {
case Success(s) => {
if (s.email == "") {
fail("Email must not be blank")
} else {
succeed(s)
}
}
case Failure(f) => fail(f)
}
}
case Failure(f) => fail(f)
}
}
def updateDB(request: Request): Unit = {
throw new RuntimeException("Fake DB Error")
()
}
val updateDBStep: Request => TwoTrack[Request] =
tryCatch(tee(updateDB))(ex => ex.getMessage)
def canonicalizeEmail(request: Request): Request = {
request.copy(email = request.email.trim().toLowerCase())
}
def main(args: Array[String]): Unit = {
val railway =
validateRequest
.andThen(map2(canonicalizeEmail))
.andThen(bind(updateDBStep))
.andThen(log)
val request = Request(name = "", email = "")
railway(request)
}
}
object RailwayList {
sealed trait TwoTrack[F]
case class Success[S](data: S) extends TwoTrack[S]
case class Failure[S](messages: List[String]) extends TwoTrack[S]
def succeed[S](x: S) = Success(x)
def fail[S](message: String) = Failure[S](List(message))
def fail[S](messages: List[String]) = Failure[S](messages)
def bind[A, B](switchFunction: A => TwoTrack[B]): TwoTrack[A] => TwoTrack[B] = {
{ (twoTrackInput: TwoTrack[A]) =>
twoTrackInput match {
case Success(s) => switchFunction(s)
case Failure(f) => fail(f)
}
}
}
def map[A, B](singleTrackFunction: A => B): TwoTrack[A] => TwoTrack[B] = { twoTrackInput: TwoTrack[A] =>
twoTrackInput match {
case Success(s) => succeed(singleTrackFunction(s))
case Failure(f) => fail(f)
}
}
def map2[A, B](singleTrackFunction: A => B): TwoTrack[A] => TwoTrack[B] = {
bind(singleTrackFunction.andThen(succeed))
}
def tee[A](deadEndFunction: A => Unit)(a: A): A = {
deadEndFunction(a)
a
}
def tryCatch[A, B](f: A => B)(exnHandler: Throwable => String)(x: A): TwoTrack[B] = try {
succeed(f(x))
} catch {
case ex: Throwable =>
fail(exnHandler(ex))
}
def doubleMap[A, B](successFunc: A => B)
(failureFunc: List[String] => List[String])
(twoTrackInput: TwoTrack[A]): TwoTrack[B] = twoTrackInput match {
case Success(s) => succeed(successFunc(s))
case Failure(f) => fail(failureFunc(f))
}
def log[A](twoTrackInput: TwoTrack[A]): TwoTrack[A] = {
val success = { x: A => println(s"DEBUG. Success so far: $x"); x }
val failure = { xs: List[String] => println(s"ERROR. ${ xs.mkString("; ") }"); xs }
doubleMap(success)(failure)(twoTrackInput)
}
def plus[A, B](addSuccess: (B, B) => B,
addFailure: (List[String], List[String]) => List[String],
switch1: A => TwoTrack[B],
switch2: A => TwoTrack[B])
(x: A): TwoTrack[B] = {
(switch1(x), switch2(x)) match {
case (Success(s1), Success(s2)) => Success(addSuccess(s1, s2))
case (Failure(f1), Success(_)) => Failure(f1)
case (Success(_), Failure(f2)) => Failure(f2)
case (Failure(f1), Failure(f2)) => Failure(addFailure(f1, f2))
}
}
// ---
case class Request(name: String, email: String)
def nameNotBlank: Request => TwoTrack[Request] = { request: Request =>
if (request.name == "") {
fail("Name must not be blank")
} else {
succeed(request)
}
}
def name50: Request => TwoTrack[Request] = { request: Request =>
if (request.name.length > 50) {
fail("Name must not be longer than 50 chars")
} else {
succeed(request)
}
}
def emailNotBlank: Request => TwoTrack[Request] = { request: Request =>
if (request.email == "") {
fail("Email must not be blank")
} else {
succeed(request)
}
}
sealed case class ComposableSwitch[A, B](f1: A => TwoTrack[B]) {
def &&&(f2: A => TwoTrack[B]): A => TwoTrack[B] = {
val addSuccess: (B, B) => B = (r1: B, _: B) => r1
val addFailure: (List[String], List[String]) => List[String] = (s1: List[String], s2: List[String]) => s1 ++ s2
plus(addSuccess, addFailure, f1, f2)
}
}
implicit def functionToComposableFunction[A, B](f: A => TwoTrack[B]) = ComposableSwitch(f)
def validateRequest: Request => TwoTrack[Request] =
nameNotBlank &&& name50 &&& emailNotBlank
def validateRequest_inlined(input: Request): TwoTrack[Request] = {
val nameNotBlankResult = if (input.name == "") {
fail("Name must not be blank")
} else {
succeed(input)
}
nameNotBlankResult match {
case Success(s) => {
val name50Result = if (s.name.length > 50) {
fail("Name must not be longer than 50 chars")
} else {
succeed(s)
}
name50Result match {
case Success(s) => {
if (s.email == "") {
fail("Email must not be blank")
} else {
succeed(s)
}
}
case Failure(f) => fail(f)
}
}
case Failure(f) => fail(f)
}
}
def updateDB(request: Request): Unit = {
throw new RuntimeException("Fake DB Error")
()
}
val updateDBStep: Request => TwoTrack[Request] =
tryCatch(tee(updateDB))(ex => ex.getMessage)
def canonicalizeEmail(request: Request): Request = {
request.copy(email = request.email.trim().toLowerCase())
}
def main(args: Array[String]): Unit = {
val railway =
validateRequest
.andThen(map2(canonicalizeEmail))
.andThen(bind(updateDBStep))
.andThen(log)
val request = Request(name = "", email = "")
railway(request)
}
}
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