added scanLeft

geny/src/geny/Generator.scala

@@ -83,6 +83,7 @@ trait Generator[+A]{
     result
   }
 
+  def scanLeft[B](start: B)(f: (B,A) => B): Generator[B] = new Generator.Scanned(this,start,f)
 
   def reduce[B >: A](f: (B, A) => B): B = reduceLeft(f)
   def reduceLeft[B >: A](f: (B, A) => B): B = {
@@ -297,6 +298,16 @@ object Generator{
     override def toString = s"$inner.map($func)"
   }
 
+  private class Scanned[+T, V](inner: Generator[V], initial: T, func: (T,V) => T) extends Generator[T]{
+    def generate(f: T => Generator.Action) = {
+      var acc = initial
+      inner.generate{ v =>
+        acc = func(acc,v)
+        f(acc)
+      }
+    }
+  }
+
   private class Sliced[+T](inner: Generator[T], start: Int, end: Int) extends Generator[T]{
     def generate(f: T => Generator.Action) = {
       var count = 0

geny/test/src/geny/TestGenerator.scala

@@ -62,6 +62,10 @@ object TestGenerator extends TestSuite{
         assert(Generator.from[IndexedSeq, Int](0 until 10).foldLeft(0)(_ + _) == 45)
         assert(Generator.from[IndexedSeq, Int](0 until 0).foldLeft(0)(_ + _) == 0)
       }
+      test("scanLeft"){
+        assert(Generator(1,2,3,4).scanLeft(100)(_ + _).toList == List(101,103,106,110))
+        assert(Generator[Int]().scanLeft(100)(_ + _).toList == List())
+      }
 
 
       test("concat"){