errorp 
NAME 
errorp() - determine whether or not a given variable is an error code
SYNOPSIS 
int errorp( mixed arg );
DESCRIPTION 
Returns 1 if 'arg' is an integer that is an error code.
Eventually  efuns  will  be  modified to return standard error codes so
that code like this will be possible:
    if (errorp(result = efun_call()))
        printf("error = %d\n", result);
In future, there will also be a perror(result)  efun  to  return  error
string that goes with a particular error integer.
SEE ALSO 
nullp(3), undefinedp(3)