ocaml-lib-devel

[Ocaml-lib-devel] Dllist skip negative arguments

[Pierre-Antoine D. <de...@LP...>]

Hello people,

Is it normal that I can't have Dllist.skip work as I expect using 
negative arguments ?

Here is an exemple of what I'm trying with extlib 1.4 :

 > ocaml  -I /<path_to_extlib>/ /<path_to_extlib>/extLib.cma

let ll = Dllist.create 0;;
Dllist.add ll 4;;
Dllist.add ll 8;;
Dllist.add ll 5012;;
let printl a = print_string ((string_of_int a)^"\n");;
Dllist.iter printl ll;;
let ll1 = Dllist.skip ll 1;;
Dllist.iter printl ll1;;
let ll1m = Dllist.skip ll (-1);;
Dllist.iter printl ll1m;;


I expect the operation on ll1 and ll1m to behave differently, however I 
have exactly the same result ... as if the negative sign was not taken 
into account.

Am I doing something wrong ?

Thanks for your help.

PA.

Re: [Ocaml-lib-devel] Dllist skip negative arguments

[Amit D. <ami...@gm...>]

Looking at Dllist.skip, this looks like a bug. A better implementation of
skip might be:

let skip node idx =3D
let rec loop idx n =3D
if idx =3D=3D 0 then
n
else if idx>0 then
loop (idx -1) n.next
else
loop (idx + 1) n.prev
in
loop idx node

(The current version doesn't use n.prev for negative arguments). If there
are no complains, I'll make this change.



On 10/3/05, Pierre-Antoine Delsart <de...@lp...> wrote:
>
>
> Hello people,
>
> Is it normal that I can't have Dllist.skip work as I expect using
> negative arguments ?
>
> Here is an exemple of what I'm trying with extlib 1.4 :
>
> > ocaml -I /<path_to_extlib>/ /<path_to_extlib>/extLib.cma
>
> let ll =3D Dllist.create 0;;
> Dllist.add ll 4;;
> Dllist.add ll 8;;
> Dllist.add ll 5012;;
> let printl a =3D print_string ((string_of_int a)^"\n");;
> Dllist.iter printl ll;;
> let ll1 =3D Dllist.skip ll 1;;
> Dllist.iter printl ll1;;
> let ll1m =3D Dllist.skip ll (-1);;
> Dllist.iter printl ll1m;;
>
>
> I expect the operation on ll1 and ll1m to behave differently, however I
> have exactly the same result ... as if the negative sign was not taken
> into account.
>
> Am I doing something wrong ?
>
> Thanks for your help.
>
> PA.
>
>
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Re: [Ocaml-lib-devel] Dllist skip negative arguments

[Brian H. <bh...@sp...>]

On Tue, 4 Oct 2005, Amit Dubey wrote:

> Looking at Dllist.skip, this looks like a bug. A better implementation of
> skip might be:
>
> let skip node idx =
> let rec loop idx n =
> if idx == 0 then
> n
> else if idx>0 then
> loop (idx -1) n.next
> else
> loop (idx + 1) n.prev
> in
> loop idx node
>
> (The current version doesn't use n.prev for negative arguments). If there
> are no complains, I'll make this change.

I'm wondering if it might not be better to split the two loops, to avoid 
taking repeated branchs:

let skip node idx =
 	let rec floop idx n =
 		if idx == 0 then
 			n
 		else
 			floop (idx-1) n.next
 	in
 	let rec bloop idx n =
 		if idx == 0 then
 			n
 		else
 			bloop (idx-1) n.prev
 	in
 	if idx == 0 then
 		n
 	else if idx > 0 then
 		floop (idx-1) n.next
 	else
 		bloop ((-idx)-1) n.prev
;;

Brian

Re: [Ocaml-lib-devel] Dllist skip negative arguments

[Amit D. <ami...@gm...>]

Good point. I'll use this version. Hmmm... maybe I should add a unit test
for skip as well...

-Amit

On 10/4/05, Brian Hurt <bh...@sp...> wrote:
>
>
>
> On Tue, 4 Oct 2005, Amit Dubey wrote:
>
> > Looking at Dllist.skip, this looks like a bug. A better implementation
> of
> > skip might be:
> >
> > let skip node idx =3D
> > let rec loop idx n =3D
> > if idx =3D=3D 0 then
> > n
> > else if idx>0 then
> > loop (idx -1) n.next
> > else
> > loop (idx + 1) n.prev
> > in
> > loop idx node
> >
> > (The current version doesn't use n.prev for negative arguments). If
> there
> > are no complains, I'll make this change.
>
> I'm wondering if it might not be better to split the two loops, to avoid
> taking repeated branchs:
>
> let skip node idx =3D
> let rec floop idx n =3D
> if idx =3D=3D 0 then
> n
> else
> floop (idx-1) n.next
> in
> let rec bloop idx n =3D
> if idx =3D=3D 0 then
> n
> else
> bloop (idx-1) n.prev
> in
> if idx =3D=3D 0 then
> n
> else if idx > 0 then
> floop (idx-1) n.next
> else
> bloop ((-idx)-1) n.prev
> ;;
>
> Brian
>
>