Difference between "let rec" and just "let"?

Difference between "let rec" and just "let"?

[circ ular]

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
#

Re: [Caml-list] Difference between "let rec" and just "let"?

[Jean Krivine]

Each time you use let, you can also use let rec, but you have to use
the rec (for recursive) if you want to declare a recursive function as
in:
let rec f x = if x<0 then 0 else x * f(x-1)


On Wed, Aug 13, 2008 at 8:49 AM, circ ular <circularfunc@gmail.com> 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
> #
>
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Re: [Caml-list] Difference between "let rec" and just "let"?

[Christophe TROESTLER]

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.

Re: [Caml-list] Difference between "let rec" and just "let"?

[Andrej Bauer]

Jean Krivine wrote:
> Each time you use let, you can also use let rec,

Not quite. For example:

let x = 5 in
let x = x + 10 in
  x

is not equivalent to

let rec x = 5 in
let rec x = x + 10 in
  x

(In fact the second one doesn't compile.)

Andrej