Re: [Caml-list] Function returning recursive lists

[Ashish Agarwal <agarwal1975@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1706 bytes --]

It would be nice to have metaocaml as one of the available compilers in
opam. Anyone thinking of doing that?

On Wed, Dec 19, 2012 at 6:50 PM, Jeremy Yallop <yallop@gmail.com> wrote:

> On 19 December 2012 22:23, Philippe Wang <mail@philippewang.info> wrote:
> > I have a (somehow silly) answer to your question:
> >
> > let gen_make_circ n =
> >   Printf.printf "let make_circ = function [] -> []\n";
>
> That's an interesting idea, Philippe.  Here's an approach along the
> same lines using MetaOCaml.
>
>   let rec docycle l =
>    .!(.< let rec s =
>           .~(let rec loop = function
>                | [] -> .< s >.
>                | x :: xs -> .< x :: .~(loop xs) >.
>              in loop l)
>          in s >.)
>
> The essential idea is the same as in your code: dynamically generating
> a suitable 'let rec' expression.  However, MetaOCaml also helpfully
> guarantees that the generated code is well-formed and well-typed, and
> makes it possible to compile and run the generated code without
> leaving the language.
>
> Here's the code in action:
>
>     # docycle;;
>     - : 'a list -> 'a list = <fun>
>     # docycle [1;2;3];;
>     - : int list = [1; 2; 3; 1; 2; 3; 1; 2; 3; 1; 2; 3; 1; 2; 3; 1; 2;
> 3; 1; ...]
>     # docycle [1;2;3;4;5];;
>     - : int list = [1; 2; 3; 4; 5; 1; 2; 3; 4; 5; 1; 2; 3; 4; 5; 1; 2;
> 3; 4; ...]
>
> (For the sake of simplicity I haven't handled the case where the input
> list is empty, but that's not difficult to do.)
>
> --
> Caml-list mailing list.  Subscription management and archives:
> https://sympa.inria.fr/sympa/arc/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
>

[-- Attachment #2: Type: text/html, Size: 2520 bytes --]