src/Pure/Isar/outer_syntax.scala

       case Token.Parsers.Success(tokens, _) => tokens
       case _ => error("Unexpected failure of tokenizing input:\n" + input.toString)
     }
   }
 
-  def scan_line(input: CharSequence, context: Scan.Line_Context): (List[Token], Scan.Line_Context) =
+  def scan_line(input: CharSequence, context: Scan.Line_Context, depth: Int)
+    : (List[Token], Scan.Line_Context, Int) =
   {
     var in: Reader[Char] = new CharSequenceReader(input)
     val toks = new mutable.ListBuffer[Token]
     var ctxt = context
     while (!in.atEnd) {

         case Token.Parsers.Success((x, c), rest) => { toks += x; ctxt = c; in = rest }
         case Token.Parsers.NoSuccess(_, rest) =>
           error("Unexpected failure of tokenizing input:\n" + rest.source.toString)
       }
     }
-    (toks.toList, ctxt)
+
+    val depth1 = depth // FIXME
+    (toks.toList, ctxt, depth1)
   }
 
 
   /* parse_spans */