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trait Generator[+T] {
  self =>
 
  def generate: T
 
  def map[S](f: T => S): Generator[S] = new Generator[S] {
    def generate = f(self.generate)
  }
 
  def flatMap[S](f: T => Generator[S]): Generator[S] = new Generator[S] {
    def generate: S = f(self.generate).generate
  }
}
 
val numbers = new Generator[Int] {
  val rand = new java.util.Random
  def generate = rand.nextInt()
}
val booleans = for ( n <- numbers ) yield (n > 0)
println(numbers.generate)
println(booleans.generate)
trait Tree
case class Inner(l: Tree, r: Tree) extends Tree
case class Leaf(n: Int) extends Tree
 
def trees: Generator[Tree] = for {
  isLeaf <- booleans
  tree <- if (isLeaf) leafs else innerNodes
} yield tree
 
 
def leafs = for {
  n <- numbers
} yield Leaf(n)
def innerNodes = for {
  l <- trees
  r <- trees
} yield Inner(l, r)
 
 
 
println(Leaf(5))

/opt/scala/bin/scalac: line 50: /dev/null: Permission denied
Main.scala:15: error: expected class or object definition
val numbers = new Generator[Int] {
^
Main.scala:19: error: expected class or object definition
val booleans = for ( n <- numbers ) yield (n > 0)
^
Main.scala:20: error: expected class or object definition
println(numbers.generate)
^
Main.scala:21: error: expected class or object definition
println(booleans.generate)
^
Main.scala:26: error: expected class or object definition
def trees: Generator[Tree] = for {
^
Main.scala:32: error: expected class or object definition
def leafs = for {
^
Main.scala:35: error: expected class or object definition
def innerNodes = for {
^
Main.scala:42: error: expected class or object definition
println(Leaf(5))
^
8 errors found
spoj: The program compiled successfully, but Main.class was not found.
      Class Main should contain method: def main(args: Array[String]).

Standard output is empty