gistfile1.scala

/* Basic example */
@workflow[List] val x = List(1, 2) * List(4, 5)

/* Using @context */
@context[Option] object optionExamples {
  $(Some(42) + 1) should equal (Some(43))
  $(Some(10) + Some(5) * Some(2)) should equal (Some(20))
}

@context[List] object listExamples {
  $(List(1, 2, 3) * 2) should equal (List(2, 4, 6))
  $(List("a", "b") + List("x", "y")) should equal (List("ax", "ay", "bx", "by"))
}

/* Providing workflow instances */
@context(zipList) object zipListExample {
  $(List(1, 2, 3, 4) * List(2, 3, 4)) should equal (List(2, 6, 12))
}

@context(map[String]) object mapExample {
  $(Map("foo" → 10, "bar" → 5) * 2) should equal (Map("foo" → 20, "bar" → 10))
}

@context(function[String]) object functionExample {
  val chars   = (s: String) ⇒ s.length
  val letters = (s: String) ⇒ s.count(_.isLetter)
  val nonletters = $(chars - letters)
  nonletters("R2-D2") should equal (3)
}

/* Using more complex expressions */
def divide(x: Double, y: Double) = if (y == 0) None else Some(x / y)

@workflow[Option] val teen = {
  val x = divide(1, 2)
  val y = divide(4, x)
  divide(y, x)
}
teen should equal (Some(16))

/* Annotating a method */
@context(function[Env] $ option)
def eval: Expr ⇒ Env ⇒ Option[Int] = {
  case Var(x) ⇒ fetch(x)
  case Val(value) ⇒ $(value)
  case Add(x, y) ⇒ $(eval(x) + eval(y))
}

/* Shorthand annotations */
@frp object frpExample { // same as @context(frp)
  val a = $(10)
  val b = $(5)
  val c = $(a + b * 2)

  (c!) should equal (20)

  b := 7

  (c!) should equal (24)
}

/* Stack language made easy */
@workflow(stackLang) val program = { put(5); dup; put(7); rot; sub }
execute(program) should equal(Right(List(2, 5)))

/* Point-free notation */
val isLetter: Char ⇒ Boolean = _.isLetter
val isDigit:  Char ⇒ Boolean = _.isDigit

@workflow(function[Char])
val isLetterOrDigit = isLetter || isDigit

val sqr: Double ⇒ Double = x ⇒ x * x
val log: Double ⇒ Double = x ⇒ math.log(x)

@context(function[Double])
val g = log andThen $((sqr - 1) / (sqr + 1)) // (sqr(log(x)) - 1) / (sqr(log(x)) + 1)

/* Purely functional logging */
@workflow(writer[Log])
val Writer(result, logEntries) = {
  log("Lets define a variable")
  val x = 2

  log("And calculate a square of it")
  val square = x * x

  log("Also a cube and add them together")
  val cube = x * x * x
  val sum = square + cube

  log("This is all so silly")
  30 / 5
}

result should equal (6)
logEntries should equal (Log(List("Lets define a variable",
                                  "And calculate a square of it",
                                  "Also a cube and add them together",
                                  "This is all so silly")))