The issue is that this definition can't be generalized to lists of
arbitrary size.
The code
let list_cycle l =
let rec loop = l @ loop in
loop
will not be accepted.
I don't know the exact rule, but I guess that on the right-hand side
of a
let rec defining a ground value named foo you can only write a term
which
evaluates to a finite ground term on the currently defined variables +
foo.
That is to say something that evaluates to a finite tree of
constructors with
constants or defined variables as leaves.
Maybe someone more knowledgeable could state the exact rule.
- marc
P.S. : the code using Obj is far from a solution as it modifies the
existing structure
of the list to add cycling and thus, breaks persistency.
Le 23 oct. 2009 à 17:35, Damien Guichard a écrit :
let list_cycle2 a b =
let rec loop = a::b::loop
in loop
- damien
En réponse au message
de : Lukasz Stafiniak
du : 2009-10-23 01:10:37
À : caml-list
CC :
Sujet : Re: [Caml-list] forbidden construct as right hand side of
"let rec"
While we are at it, what is the best way to convert a "straight" list
into a cyclic list?
i.e. convert
let l = a::b::[]
into
let rec l = a::b::l
(for arbitrary length lists). (The answer I recall from the archives
was using Obj.magic to mutate the [] in the original list).
On Fri, Oct 23, 2009 at 12:34 AM, Stéphane Glondu <st...@glondu.net
> wrote:
> Mathias Kende a écrit :
> > let rec g = f g
>
> What about:
>
> let rec g x = f g x
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