.help error, fatal, errchk, erract, iferr 2 "Error Handling Strategy"
.sh
ERROR HANDLING

    A recoverable error condition is asserted with ERROR.  An irrecoverable
error condition is asserted with FATAL.  Error recovery is implemented
using the IFERR and IFNOERR statements in the preprocessor language.
ERRACT may be called in an IFERR statement to cause a warning to be issued,
or to cause a particular error action to be taken.  ERRCODE returns either
OK or the integer code of the posted error.

Language support includes the IFERR and IFNOERR statements and the ERRCHK
declaration.  The IFERR statement is grammatically equivalent to the IF
statement.  Note that the condition to be tested in an IFERR statement may
be a procedure call or assignment statement, while the IF statement tests
a boolean expression.


.nf
	errchk	proc1, proc2, ...		# errchk declaration

	iferr (procedure call or assignment statement)
	    <error_action_statement>

	iferr {
	    <any statements, including IFERR>
	} then
	    <error_action_statement>


Library procedures (ERROR and FATAL cause a RETURN):

	  error (errcode, error_message)
	  fatal (errcode, error_message)
	 erract (severity)
  val = errcode ()


ERRACT severity codes (<error.h>):

	EA_WARN			# issue a warning message
	EA_ERROR		# assert recoverable error
	EA_FATAL		# assert fatal error
.fi


An arithmetic exception (X_ARITH) will be trapped by an IFERR statement,
provided the posted handler(s) return without causing error restart.
X_INT and X_ACV may only be caught by posting an exception handler with
XWHEN.