arrays and type variables...

arrays and type variables...

[Don Syme]

Shouldn't "[| [] |]" count as a value??

bash$ ocaml
        Objective Caml version 2.00

# let x = [| [] |];;
val x : '_a list array = [|[]|]
# let x = [];;
val x : 'a list = []
# let x = [| |];;
val x : 'a array = [||]
#

Cheers,
Don

Re: arrays and type variables...

[Pierre Weis]

> Shouldn't "[| [] |]" count as a value??
> 
> bash$ ocaml
>         Objective Caml version 2.00
> 
> # let x = [| [] |];;
> val x : '_a list array = [|[]|]
[...]
> Cheers,
> Don

No, we can't, since it is equivalent to create a polymorphic reference
(you just have to put the value into a list and to assign this list to
the vector). This would break the type system's safety theorem: it
would lead to ``bus errors''.

Best regards,

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://cristal.inria.fr/~weis/

Re: arrays and type variables...

[Andreas Rossberg]

Don Syme wrote:
> 
> Shouldn't "[| [] |]" count as a value??
> 
> # let x = [| [] |];;
> val x : '_a list array = [|[]|]
> # let x = [];;
> val x : 'a list = []
> # let x = [| |];;
> val x : 'a array = [||]

No, because you can assign to arrays:

# let x = [| [] |];;
val x : '_a list array = [|[]|]
# x.(0) <- [1];;
- : unit = ()
# x;;
- : int list array = [|[1]|]

You cannot assign anything to the empty array [| |], however.

Regards,

	- Andreas

-- 
Andreas Rossberg, rossberg@ps.uni-sb.de

:: be declarative. be functional. just be. ::