#Json #Reads a #JsArray & map on each elements of the array applying provided Reads (cumulative errors) #Play2.1

code.scala

// Reads a JsArray and then map on its elements applying Reads (cumulating errors)
def readJsArrayMap[A <: JsValue](transformEach: Reads[A]): Reads[JsArray] = Reads { js => js match {
  case arr: JsArray =>
    arr.value.foldLeft(JsSuccess(Seq[JsValue]()): JsResult[Seq[JsValue]]) { (acc, e) =>
    acc.flatMap{ seq =>
      e.transform(transformEach).map( v => seq :+ v )
    }
  }.map(JsArray(_))
  
  case _ => JsError("expected JsArray")
}}

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