src/Pure/System/process_result.scala

   def was_timeout: Process_Result = copy(rc = 1, timeout = true)
 
   def ok: Boolean = rc == 0
   def interrupted: Boolean = rc == Exn.Interrupt.return_code
 
-  def check: Process_Result =
-    if (ok) this
+  def check_rc(pred: Int => Boolean): Process_Result =
+    if (pred(rc)) this
     else if (interrupted) throw Exn.Interrupt()
     else Exn.error(err)
+
+  def check: Process_Result = check_rc(_ == 0)
 
   def print: Process_Result =
   {
     Output.warning(err)
     Output.writeln(out)