def setFailAction( self, fn ):
self.failAction = fn<EOL>return self<EOL>
Define action to perform if parsing fails at this expression.
           Fail acton fn is a callable function that takes the arguments
           ``fn(s,loc,expr,err)`` where:
           - s = string being parsed
           - loc = location where expression match was attempted and failed
           - expr = the parse expression that failed
           - err = the exception thrown
           The function returns no value.  It may throw :class:`ParseFatalException`
           if it is desired to stop parsing immediately.