Re: [Caml-list] Subtyping (or something like it)

[Reed Wilson <cedilla@gmail.com>]

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I hadn't noticed that 4.06 will let me extend indexing. It's certainly a
nice feature to have; I'll throw it in :)
I actually think I can use that to great effect - a lot of this is used to
pack data into structures which are sent to/from C, the network, files,
etc.. Having multiple ways of indexing it could be quite helpful for
getting/setting multiple different types of data.
let ( .!{ } ) = get_1byte_int
let ( .@{ } ) = get_2byte_int
let ( .${ } ) = get_4byte_int
let ( .*{ } ) = get_8byte_int
Where the extension character is shift+number of bytes (at least on my
keyboard...) I'm a bit worried that it'll start looking like Perl, but time
will tell.
Thanks for the great ideas!

On Fri, Nov 17, 2017 at 5:01 AM, octachron <octa@polychoron.fr> wrote:

> With OCaml 4.06, if what you really want is to have a nice syntax for
> array indexing, one solution would be to define your own indexing operators:
>
>   let (  .%{ } ) a k = a.{k}
>   let ( .%{ } <- ) a k x = a.{k} <- x
>
> These operators can be used like standard indexing operators
>
>     let x = a.%{ 0 } in
>     a.%{ 1 } <- x
>
> and exported with
>
>    val (  .%{ } ): …
>    val ( .%{ } <- ): …
>
> Nevertheless, contrarily to Bigarray, there is no implicit conversion for
> multidimensional array,
> in other words
>
>     a .%{0,1}
>
> will not work out of the box.
>
> However, if needed, it is possible to use qualified indexing operators to
> circumvent this difficulty:
>
>   module D1 = struct let ( .%{} ) a k = a.{k} end
>   module D2 = struct let ( .%{} ) a (k,l) = a.{k,l} end
>   let x_ij = mat.D2.%{i, j}
>   let x_0 = vector.D1.%{0}
>
> See also the manual for more details: http://caml.inria.fr/pub/docs/
> manual-ocaml/extn.html#s%3Aindex-operators .
>
> − octachron.
>
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