On Monday 10 March 2008 17:49:06 stevewirts wrote:
> could anyone tell me if this is tail recursive?
>
> let append l1 l2 =
> let rl1 = List.rev l1 in
> let rec rappend l1 l2 =
> if l1 = [] then l2
> else
> let hd = List.hd l1 in
> let tl = List.tl l1 in
> let larger = hd :: l2 in
> rappend tl larger
> in rappend rl1 l2;;
>
> # append [1;2;3] [4;5;6];;
> - : int list = [1; 2; 3; 4; 5; 6]
That is tail recursive but you can write it much more elegantly using pattern
matching:
let rec rev_append l1 l2 =
match l1, l2 with
| [], l2 -> l2
| hd::tl, l2 -> rev_append tl (hd::l2);;
let append l1 l2 =
rev_append (List.rev l1) l2;;
Note that you already have:
# [1;2;3] @ [4;5;6];;
- : int list = [1; 2; 3; 4; 5; 6]
--
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/products/?e
