An application reset istrm replaces the current state of istrm with
the value supplied when istrm was constructed.
FAILURE
Never fails.
EXAMPLE
- reset(next(next
(mk_istream (fn x => x+1) 0 (concat "gsym" o int_to_string))));
> val it = <istream> : (int, string) istream
- state it;
> val it = "gsym0" : string
COMMENTS
Perhaps the type of reset should be ('a,'b) istream -> unit.