Re: [Caml-list] let mutable (was OCaml Speed for Block Convolutions)

[Michel Quercia <michel.quercia@prepas.org>]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="US-ASCII", Size: 1469 bytes --]

Le Vendredi  8 Juin 2001 19:30,  Pierre Weis a écrit :

> The introduction of a ``let mutable'', more concisely noted with the
> var keyword, is not new: it has been discussed in the Caml groups 3 or
> 4 years ago. We chose to abandon it for sake of semantics simplicity
> of the language.

For beginners (f.e. students) things look a bit complicated :

(* summing up all elements of an integer array *)
let adda a =
  let res = ref 0 in
  let i = ref 0 in
  while !i < Array.length(a) do res := !res+a.(!i); i := !i+1 done;
  !res
;;

A lot of boring exclam, but that's the price to pay for having 
mutable values, and that's logical. Okay ...

(* same, but with a for loop *)
let add_1 a =
  let res = ref 0 in
  for i=0 to Array.length(a)-1 do res := !res + a.(i) done;
  !res
;;

No exclam and no ref for i ?  And its value is changing though ? Where is 
gone the logic ?

> This construction would have introduced the notion of
> Lvalue in Caml, thus introducing some additional semantics complexity,
> and a new notion to explain to beginners.

Lvalues already exist in Ocaml (and have to be explained to beginners), for 
example : "a.(i) <- a.(i)+1".

Regards,
-- 
Michel Quercia
23 rue de Montchapet, 21000 Dijon
http://pauillac.inria.fr/~quercia
mailto:michel.quercia@prepas.org
-------------------
Bug reports: http://caml.inria.fr/bin/caml-bugs  FAQ: http://caml.inria.fr/FAQ/
To unsubscribe, mail caml-list-request@inria.fr  Archives: http://caml.inria.fr