SET(SPECIAL_ERROR_SYMBOL)

  Designates the global variable that you want TPU to set to 0 when a
  case-style error handler handles a CTRL/C.

  Syntax

  SET (SPECIAL_ERROR_SYMBOL, string)

  Parameter

     string     The name of the global variable that you want TPU to set
                to 0 when an error handler handles a CTRL/C.

  Comments

     Once you designate the variable that is to be the special error symbol,
     TPU sets the variable to 0 if either of the following events occur:

      o  TPU executes the TPU$_CONTROLC selector in a case-style error
         handler, or

      o  TPU executes the OTHERWISE clause in a case-style error handler
         and does not encounter a RETURN statement

     You can only use SET (SPECIAL_ERROR_SYMBOL) once in a program.  You
     must declare or create the variable before you use it in the SET
     statement.  TPU does not clear the variable in response to
     non-case-style error handlers.

     The variable specified by SET (SPECIAL_ERROR_SYMBOL) can be used to
     determine whether TPU has exited from current procedures and has
     returned to waiting for a new keypress.

  Example

     The following statement designates the global variable "mork" as the
     variable to be cleared if TPU executes the TPU$_CONTROLC selector in
     a case-style error handler:

     SET (SPECIAL_ERROR_SYMBOL, mork)