Re: [Caml-list] Re: How to read different ints from a Bigarray?

[Goswin von Brederlow <goswin-v-b@web.de>]

blue storm <bluestorm.dylc@gmail.com> writes:

> On Wed, Oct 28, 2009 at 6:57 PM, Goswin von Brederlow <goswin-v-b@web.de> wrote:
>> Maybe ideal would be a format string based interface that calls C with
>> a format string and a record of values. Because what I really need is
>> to read/write records in an architecture independend way. Something
>> like
>>
>> type t = { x:int; y:char; z:int64 }
>> let t_format = "%2u%c%8d"
>>
>> put_formated buf t_format t
>>
>> But how to get that type safe? Maybe a camlp4 module that generates
>> the format string and type from a single declaration so they always
>> match.
>
> It's possibly off-topic, but you might be interested in Richard
> Jones's Bitstring project [1] wich deals with similar issues quite
> nicely in my opinion.
>
> [1] http://code.google.com/p/bitstring/

No, quite on-topic.

I glanced at the examples and code and it looks to me though as if
this can only parse bitstrings but not create them from a pattern.
You have

let parse_foo bits =
  bitmatch bits with
  | { x : 16 : littleendian; y : 16 : littleendian } -> fun x y -> (x, y)

but no

let unparse_foo (x, y) =
  bitmake { x : 16 : littleendian; y : 16 : littleendian } x y


Idealy would be something along

let pattern = make_pattern { x : 16 : littleendian; y : 16 : littleendian }
let parse_foo bits = parse pattern (fun x y -> (x, y))
let unparse_foo (x, y) = unparse pattern x y

But I know how to do that with CPS already. I just need the primitives
to get/set the basic types.

MfG
        Goswin