src/Pure/General/json.scala

 
     def apply(json: T): S =
     {
       val result = new StringBuilder
 
-      def string(s: String)
+      def string(s: String): Unit =
       {
         result += '"'
         result ++=
           s.iterator.map {
             case '"'  => "\\\""

               else c
           }.mkString
         result += '"'
       }
 
-      def array(list: List[T])
+      def array(list: List[T]): Unit =
       {
         result += '['
         Library.separate(None, list.map(Some(_))).foreach({
           case None => result += ','
           case Some(x) => json_format(x)
         })
         result += ']'
       }
 
-      def object_(obj: Object.T)
+      def object_(obj: Object.T): Unit =
       {
         result += '{'
         Library.separate(None, obj.toList.map(Some(_))).foreach({
           case None => result += ','
           case Some((x, y)) =>

             json_format(y)
         })
         result += '}'
       }
 
-      def json_format(x: T)
+      def json_format(x: T): Unit =
       {
         x match {
           case null => result ++= "null"
           case _: Int | _: Long | _: Boolean => result ++= x.toString
           case n: Double =>