English version
Accueil     À propos     Téléchargement     Ressources     Contactez-nous    

Ce site est rarement mis à jour. Pour les informations les plus récentes, rendez-vous sur le nouveau site OCaml à l'adresse ocaml.org.

Browse thread
Re: [Caml-list] type generalization of recursive calls
[ Home ] [ Index: by date | by threads ]
[ Search: ]

[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
Date: 2010-02-17 (18:13)
From: Damien Guichard <alphablock@o...>
Subject: Re: [Caml-list] type generalization of recursive calls
I have to apologize because your definition is actually correct.
Sorry i have read it too fast and didn't see map burried in type casting.

It seems to me your are doing structural recursion on some binary tree structure.
Presumably to fast-merge binary heaps or something like that.
pa_polyrec is probably a must have for such things.

- damien

Le 17/02/2010 à 17:34:24, "Stéphane Gimenez" <stephane.gimenez@pps.jussieu.fr>
à écrit :
>I just realized that ocaml generalizes the type of a recursively
>defined function *only* for calls which are outside it's own
>definition. Recursive calls cannot use a generalized type.
>In fact, I'm tring to work with such a data type:
>type 'a t =
>  | E
>  | D of 'a t * 'a t
>  | O of 'a
>  | I of 'a t t
>And, I'm forced to use some dark magic to define simple operations on
>let rec map (f : 'a -> 'b) : 'a t -> 'b t =
>  begin function
>  | E -> E
>  | D (t1, t2) -> D (map f t1, map f t2)
>  | O a -> O (f a)
>  | I tt ->
>      I ((Obj.magic map : ('a t -> 'b t) -> 'a t t -> 'b t t) (map f) tt)
>  end
>  - Is it theoreticaly safe to generalize recursive calls ?
>  - Is there a syntactical trick to use generalized recursive calls ?
>  - Could such a generalization be added to the type checker ?
>      - Performance issues ?
>      - More obfusctated type checking errors ?
>In a related disscution I found, one asked about generalization
>between mutualy recursive definitions (same problem). No answers, but
>maybe I just lack pointers.
>Caml-list mailing list. Subscription management:
>Archives: http://caml.inria.fr
>Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
>Bug reports: http://caml.inria.fr/bin/caml-bugs

Mail created using EssentialPIM Free - www.essentialpim.com