RE: [Caml-list] Great Beginner

["Krishnaswami, Neel" <neelk@cswcasa.com>]

Franck [mailto:franck.collineau@francetelecom.com] wrote:
> Hello!
> I have written the following code:
> let somme(x,n)=
>     for i=1 to i=n
>         do
>         x<-x+1
>         done;;
> 
> caml tel me that i is not define. What is the problem ?

You have a couple of syntax errors. First, the syntax of a 
for-loop is 

  "for i = 1 to n do <foo> done"

Second, your assignment statement x <- x + 1 has the wrong syntax,
and the wrong type. If you want to do an assignment, you need to 
use the (:=) operator, like this:

  x := 5

(:=) has the type 'a ref -> 'a -> unit, which means that the left
hand side should be a reference, and the right hand side should be
the value you want the reference to point to. However, when you 
write:

  x := x + 1

you will get a type error, because x has type int ref, and (+) has
type int -> int -> int. So to do the addition you need to dereference 
the reference:

let somme(x, n) = 
  for i = 1 to n do
    x := !x + 1
  done

which has type int ref -> int -> unit. This doesn't look like a 
function I would want to write, but maybe you do. :)

--
Neel Krishnaswami
neelk@cswcasa.com
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