From: Christophe TROESTLER <Christophe.Troestler+ocaml@umh.ac.be>
To: circularfunc@gmail.com
Cc: OCaml Mailing List <caml-list@yquem.inria.fr>
Subject: Re: [Caml-list] Difference between "let rec" and just "let"?
Date: Wed, 13 Aug 2008 17:17:48 +0200 (CEST) [thread overview]
Message-ID: <20080813.171748.1124003908241412727.Christophe.Troestler+ocaml@umh.ac.be> (raw)
In-Reply-To: <d5f6b0140808130549m195f1247t7ecb00649d95d0bf@mail.gmail.com>
On Wed, 13 Aug 2008 14:49:30 +0200, circ ular wrote:
>
> what is the difference between "let rec" and just "let"? what does rec
> stand for?
>
> are the following defintions exactly the same? at least they seem to
> give the same results...
>
> # let rec cube x = x*x*x;;
> val cube : int -> int = <fun>
> # cube 12;;
> - : int = 1728
>
> # let cubex x = x*x*x;;
> val cubex : int -> int = <fun>
> # cubex 12;;
> - : int = 1728
> #
The difference is that for [let x = e], [x] is not known in [e] (or
else, it is a previously defined [x]). This allows the following
style (broadly used despite the thread on that topic):
let r = .... in
let r = .... r (* r of the previous line *) .... in
let r = .... r (* r of the previous line *) .... in
let r = .... r (* r of the previous line *) .... in
...
When using [let rec x = e], [x] is known in [e] which allows to define
recursive functions but also cyclic data :
let rec x = 1 :: x
Hope it helps,
C.
P.S. There exist a beginner list where these questions belong.
prev parent reply other threads:[~2008-08-13 15:17 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-08-13 12:49 circ ular
2008-08-13 13:52 ` [Caml-list] " Jean Krivine
2008-08-13 18:39 ` Andrej Bauer
2008-08-13 15:17 ` Christophe TROESTLER [this message]
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