Re: [Caml-list] String, Array, Bigarray.char

[Tom Ridge <tom.j.ridge+caml@googlemail.com>]

Ah! These are probably solutions to my problem. I shall investigate further.

Thanks

On 9 May 2013 15:21, Anil Madhavapeddy <anil@recoil.org> wrote:
> You should look at either Lwt or Core/Async, which both provide wrappers
> over Bigarray, and asynchronous alternatives to using Unix and threads.
>
> Lwt_bytes: http://ocsigen.org/lwt/api/Lwt_bytes
> Bigstring: https://ocaml.janestreet.com/ocaml-core/latest/doc/core/Bigstring.html
>
> The choice between them depends on your situation.  Lwt is an add-on
> library that interops with existing code well, whereas Core is a more
> complete stdlib replacement (with vastly more features/datastructures).
>
> -anil
>
> On 9 May 2013, at 10:14, Tom Ridge <tom.j.ridge+caml@googlemail.com> wrote:
>
>> Although I see that this won't be so easy because various functions
>> such as Unix.write have the buffer argument being of type string :(
>>
>> So at various points I seem to be forced to use strings. I suppose one
>> alternative is to reimplement the functions I use (such as Unix.write)
>> to work with arrays. Does anyone know if this has been done elsewhere?
>>
>>
>> On 9 May 2013 15:07, Tom Ridge <tom.j.ridge+caml@googlemail.com> wrote:
>>> Thanks for this information.
>>>
>>> I guess I will probably end up using arrays as much as possible. In
>>> various places I have used strings as though they were immutable
>>> arrays of byte. I guess the advantage of this approach is that strings
>>> seem more familiar than arrays (especially Bigarrays). But it is
>>> probably not much of a big deal to move to using arrays everywhere.
>>>
>>> Thanks once again
>>>
>>> Tom
>>>
>>>
>>> On 9 May 2013 14:44, Anil Madhavapeddy <anil@recoil.org> wrote:
>>>> On 9 May 2013, at 09:32, Tom Ridge <tom.j.ridge+caml@googlemail.com> wrote:
>>>>>
>>>>> Quick question: I am working a lot with arrays of byte, which at
>>>>> various points I want to view as strings, and at various points I want
>>>>> to view as arrays. The exact types involved should be discernible from
>>>>> the code below.
>>>>>
>>>>> I have some conversion functions e.g.:
>>>>>
>>>>> type myfusebuffer = (char, Bigarray.int8_unsigned_elt,
>>>>> Bigarray.c_layout) Bigarray.Array1.t
>>>>>
>>>>> module A = Bigarray.Array1
>>>>>
>>>>> (* convenience only; don't use in production code *)
>>>>> let array_of_string bs = (
>>>>>   let arr = (Array.init (String.length bs) (String.get bs)) in
>>>>>   let contents = A.of_array Bigarray.char Bigarray.c_layout arr in
>>>>>   contents)
>>>>> let (_:string -> myfusebuffer) = array_of_string
>>>>>
>>>>> This presumably takes O(n) time (where n is the length of the string
>>>>> bs). My question is: is there functionality to move values between
>>>>> these types at cost O(1)? Basically, I'm hoping that String is
>>>>> implemented as A.of_array Bigarray.char Bigarray.c_layout or
>>>>> similar...
>>>>
>>>> Strings are represented as normal OCaml values within the OCaml heap,
>>>> whereas Bigarrays are simply pointers to externally allocated memory
>>>> (via malloc).  You do therefore need to copy across them in most cases.
>>>> One quick solution is to define a subset of the String module that uses
>>>> the Bigarray accessor functions, but this isn't ideal (especially when
>>>> external libraries that use strings are involved).
>>>>
>>>> Your fusebuffer type probably means that you're working with filesystem
>>>> data.  Can you just use Bigarrays for everything, with copies to strings
>>>> only when you absolutely need to?  We haven't released this out of beta
>>>> yet, but the cstruct camlp4 extension helps map C structures to OCaml:
>>>> https://github.com/mirage/ocaml-cstruct
>>>>
>>>> -anil
>>>>
>>>>
>>>>
>>
>> --
>> Caml-list mailing list.  Subscription management and archives:
>> https://sympa.inria.fr/sympa/arc/caml-list
>> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
>> Bug reports: http://caml.inria.fr/bin/caml-bugs
>>
>