2 iserror - test whether a value is an error value
10 return zero or positive integer < 32768
13 If x is not an error value, zero is returned.
14 If x is an error value, iserror(x) returns its error type.
18 print iserror(a), iserror(2 + a), iserror(2 + "a"), iserror(2 + 3)
29 isassoc, isatty, isblk, isconfig, isdefined, iseven, isfile,
30 ishash, isident, isint, islist, ismat, ismult, isnull, isnum, isobj,
31 isobjtype, isodd, isprime, isrand, israndom, isreal, isrel,
32 issimple, issq, isstr, istype