I think with the iter-begin API, we have the the "Maxwell's Equations of Iteration". This not only works well for conses, but it extends to numbers and ranges. * lib.h (seq_iter_t): New union member ul, containing a new member lim. existing len member moved into ul union. * lib.c (seq_iter_get_vec, seq_iter_peek_vec): Adjust access of len, now wrapped in union. (seq_iter_get_range_cnum, seq_iter_peek_range_cnum, seq_iter_get_range_chr, seq_iter_peek_range_chr, seq_iter_get_range_bignum, seq_iter_peek_range_bignum, seq_iter_get_chr, seq_iter_peek_chr, seq_iter_get_num, seq_iter_peek_num): New static functions. (seq_iter_init_with_info): Support RNG object, further classifying the iteration based on the type of the from element. Support numbers and characters as iterable. (iter_begin, iter_more, iter_item, iter_step, iter_reset): Support numbers directly as unencapsulated iterators.