NUMBER:  40

  ERROR CODE:  F

  MESSAGE TEXT:  recursive I/O operation

  EXPLANATION:  While processing an I/O statement for a logical unit,
  another I/O operation on the same logical unit was attempted.  One
  of the following conditions may have occurred:

   o  A function subprogram that performs I/O to the same logical
      unit was referenced in an expression in an I/O list or variable
      format expression.

   o  An I/O statement was executed at AST level for the same logical
      unit.

   o  An exception handler (or a procedure it called) executed an I/O
      statement in response to a signal from an I/O statement for the
      same logical unit.