alternate scala implementation

Author: Arnon Rotem-Gal-Oz

scala/fold-immutable.sc

@@ -0,0 +1,31 @@
+case class Lesson(name: String, position: Option[Int] = None)
+case class Section(title: String, resetLessonPosition: Boolean, lessons: List[Lesson],position: Option[Int] = None)
+
+val  sections = List(
+  Section("Getting started", false, List(
+    Lesson("Welcome"),
+    Lesson("Installation")
+  )),
+  Section("Basic operator", false,  List(
+    Lesson("Addition / Subtraction"),
+    Lesson("Multiplication / Division"),
+  )),
+  Section("Advanced topics", true, List(
+    Lesson("Mutability"),
+    Lesson("Immutability"),
+  ))
+)
+
+
+val (newSections,_,_) = sections.foldLeft((List[Section](),0,0)){
+  case ((sections,sectionCounter :Int,lessonCounter : Int),current) =>
+    val nextSession=sectionCounter + 1
+    val lessonBase = if (current.resetLessonPosition) 0 else lessonCounter
+    val (lessons,nextLesson)=current.lessons.foldLeft((List[Lesson](),lessonBase)){
+      case ((lessons,lessonCounter :Int),currentLesson ) =>
+        val nextLesson = lessonCounter + 1
+        (lessons :+ currentLesson.copy(position=Some(nextLesson)),nextLesson)
+    }
+    (sections :+ current.copy(position = Some(nextSession),lessons=lessons),nextSession,nextLesson)
+}
+newSections