[Caml-list] self and mutually recursive functions ?

[Caml-list] self and mutually recursive functions ?

[Metalscan]

Hello all of you !

I'm wondering wether it is possible or not to have
to functions defined wich are both mutually recursive
and simply recursive.

In each of them, there would be a match with one
branch returning itself and the other one returning
the other function.

Thanks for your help.

Matthieu Dubuget
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Re: [Caml-list] self and mutually recursive functions ?

[Pierre Weis]

> Hello all of you !
> 
> I'm wondering wether it is possible or not to have
> to functions defined wich are both mutually recursive
> and simply recursive.
> 
> In each of them, there would be a match with one
> branch returning itself and the other one returning
> the other function.
> 
> Thanks for your help.
> 
> Matthieu Dubuget

Typically a FAQ question. Look at

FAQ: http://caml.inria.fr/FAQ/

If this is not enough, post to the beginners group at

http://groups.yahoo.com/group/ocaml_beginners

All the best for learning Caml.

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/


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Re: [Caml-list] self and mutually recursive functions ?

[Michel Quercia]

Le Jeudi 10 Octobre 2002 17:47, Metalscan a écrit :
> Hello all of you !
>
> I'm wondering wether it is possible or not to have
> to functions defined wich are both mutually recursive
> and simply recursive.
>
> In each of them, there would be a match with one
> branch returning itself and the other one returning
> the other function.

I'm not sure to understand your problem. Do you want something like this ?

let rec f(x) = if x = 0 then f else g and g(x) = if x = 1 then g else f;;

Such a declaration will be rejected when submitted to ocaml, but can be 
accepted if you enable recursive types:

quercia@montchapet:~/lycee/02/tp-opt-info$ ocaml
        Objective Caml version 3.06

# let rec f(x) = if x = 0 then f else g and g(x) = if x = 1 then g else f;;
This expression has type int -> 'a but is here used with type 'a
# #quit;;
quercia@montchapet:~/lycee/02/tp-opt-info$ ocaml -rectypes
        Objective Caml version 3.06

# let rec f(x) = if x = 0 then f else g and g(x) = if x = 1 then g else f;;
val f : int -> 'a as 'a = <fun>
val g : int -> 'a as 'a = <fun>
# #quit;;

I doubt that the above f and g are actualy useful, but they are accepted 
anyway.

Regards,
-- 
Michel Quercia
23 rue de Montchapet, 21000 Dijon
http://michel.quercia.free.fr (maths)
http://pauillac.inria.fr/~quercia (informatique)
mailto:michel.quercia@prepas.org

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Re: [Caml-list] self and mutually recursive functions ?

[Pietro Abate]

On Thu, Oct 10, 2002 at 05:47:38PM +0200, Metalscan wrote:
> In each of them, there would be a match with one
> branch returning itself and the other one returning
> the other function.

do you want something like that ?

let rec f1 i =
    match i with
    | 1 -> f1 (i-1)
    | 2 -> f2 (i-1)
    | a -> let _ = Printf.printf "f1 = %d\n" a in a
and f2 j = 
    match j with 
    | 1 -> f2 (j-1)
    | 2 -> f1 (j-1)
    | a -> let _ = Printf.printf "f2 = %d\n" a in a
;; 

# f1 1;;
f1 = 0
- : int = 0
# f1 2;;
f2 = 0
- : int = 0

regards,
p

-- 
pgp key: 1024D/8A091922 2000-10-18 Pietro Abate <abate@arp.anu.edu.au>
Key fingerprint = 5111 D91B 5E0C 5CE6 FDA3  5EF4 6120 E18E 8A09 1922
public key avalaible via public key server at wwwkeys.eu.pgp.net
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