Each is a macro library that converts native imperative syntax to scalaz's monadic expression.
There is a macro library Stateless Future that provides await for asynchronous programming.
await is a mechanism that transform synchronous-like code into asynchronous expressions. C# 4.5, ECMAScript 7 and Python 3.5 also support the mechanism.
The await mechanism in Stateless Future is implemented by an algorithm called CPS transform. When learning scalaz, we found that the same algorithm could be applied for any monadic expression, including Option monad, IO monad, and Future monad. So we started this project, Each.
Each is a superset of await syntax. Each supports multiple types of monads, while await only works with Future. When we perform a CPS transform for monadic expression with the Future monad, the use case looks almost the same with the await syntax in Stateless Future
For example:
import com.thoughtworks.each.Monadic._
import scalaz.std.scalaFuture._
// Returns a Future of the sum of the length of each string in each parameter Future,
// without blocking any thread.
def concat(future1: Future[String], future2: Future[String]): Future[Int] = monadic[Future] {
future1.each.length + future2.each.length
}The similar code works for other monads than Future:
import com.thoughtworks.each.Monadic._
import scalaz.std.option._
def plusOne(intOption: Option[Int]) = monadic[Option] {
intOption.each + 1
}
assertEquals(None, plusOne(None))
assertEquals(Some(16), plusOne(Some(15)))import com.thoughtworks.each.Monadic._
import scalaz.std.list._
def plusOne(intSeq: List[Int]) = monadic[List] {
intSeq.each + 1
}
assertEquals(Nil, plusOne(Nil))
assertEquals(List(16), plusOne(List(15)))
assertEquals(List(16, -1, 10), plusOne(List(15, -2, 9)))libraryDependencies += "com.thoughtworks.each" %% "each" % "0.2.0"import com.thoughtworks.each.Monadic._Scalaz has provided Option monad, you just import it.
import com.thoughtworks.each.Monadic._
import scalaz.std.option._Please import other monad instances if you need other monad.
import com.thoughtworks.each.Monadic._
import scalaz.std.option._
val Option[String] = monadic[Option] {
"Hello, Each!"
}import com.thoughtworks.each.Monadic._
import scalaz.std.option._
val name = Option("Each")
val Option[String] = monadic[Option] {
"Hello, " + name.each + "!"
}monadic blocks do not support try, catch and finally. If you want these expressions, use catchIoMonaic instead, for example:
var count = 0
val io = catchIoMonadic[IO] {
val _ = IO(()).each
try {
count += 1
(null: Array[Int])(0) // Will throw a NullPointerException
} catch {
case e: NullPointerException => {
count += 1
100
}
} finally {
count += 1
}
}
assertEquals(0, count)
assertEquals(100, io.unsafePerformIO())
assertEquals(3, count)Note that catchIoMonaic requires an implicit parameter scalaz.effect.MonadCatchIO[F], which is only provided for scalaz.effect.IO by default.