[Caml-list] string buffer as (in|out)_channel

[Caml-list] string buffer as (in|out)_channel

[Chris Hecker]

Is there any way to do something similar to the C++ string stream stuff, 
where you treat strings (or Buffer.t's) as in_ or out_channels?  The Format 
module has a formatter for strings, but there doesn't seem to be a way to 
do it with Pervasives.  Something like:

val out_channel_of_buffer : Buffer.t -> out_channel
val in_channel_of_buffer : Buffer.t -> in_channel

and maybe _of_string versions too (probably necessary because you can't 
convert a string to a buffer for the in_channel), which fill up and don't 
expand.

It'd be very useful to be able to do this.

Thanks,
Chris

PS.  Please cc me on replies, I temporarily unsubscribed from the list, thanks!

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Re: [Caml-list] string buffer as (in|out)_channel

[Yaron M. Minsky]

I think this is the kind of place where it would make sense to use the
object system.  That is, in addition to the low-level in_channel and
out_channel, which essentially serve as proxies for unix file-descriptor
based channels, there should be I/O objects with a standard signature
for files, strings, buffers, etc.  I actually have done a simple version
of this for myself as part of the SKS project, but I think something
along these lines would be useful as a standard part of ocaml, including
integration with printf and other places in the standard library that
use I/O.  

As for your precise question, I don't myself know of any way to convert
a Buffer.t to an i/o channel.

y

On Thu, 2003-07-17 at 03:05, Chris Hecker wrote:
> Is there any way to do something similar to the C++ string stream stuff, 
> where you treat strings (or Buffer.t's) as in_ or out_channels?  The Format 
> module has a formatter for strings, but there doesn't seem to be a way to 
> do it with Pervasives.  Something like:
> 
> val out_channel_of_buffer : Buffer.t -> out_channel
> val in_channel_of_buffer : Buffer.t -> in_channel
> 
> and maybe _of_string versions too (probably necessary because you can't 
> convert a string to a buffer for the in_channel), which fill up and don't 
> expand.
> 
> It'd be very useful to be able to do this.
> 
> Thanks,
> Chris
> 
> PS.  Please cc me on replies, I temporarily unsubscribed from the list, thanks!
> 
> -------------------
> To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
> Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
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-- 
|--------/            Yaron M. Minsky              \--------|
|--------\ http://www.cs.cornell.edu/home/yminsky/ /--------|

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Re: [Caml-list] string buffer as (in|out)_channel

[Issac Trotts]

Chris Hecker wrote:

>
> Is there any way to do something similar to the C++ string stream 
> stuff, where you treat strings (or Buffer.t's) as in_ or 
> out_channels?  The Format module has a formatter for strings, but 
> there doesn't seem to be a way to do it with Pervasives.  Something like:
>
> val out_channel_of_buffer : Buffer.t -> out_channel
> val in_channel_of_buffer : Buffer.t -> in_channel
>
> and maybe _of_string versions too (probably necessary because you 
> can't convert a string to a buffer for the in_channel), which fill up 
> and don't expand.
>
> It'd be very useful to be able to do this. 

For reading, this might do what you want:

(* wrap a Buffer with a Stream, for reading *)
let stream_of_buffer buf =
  Stream.of_string(Buffer.contents buf)
;;

For writing, I guess this sort of thing would do it:

module Ostream :
  sig
    type t = char -> unit
    val of_buffer : Buffer.t -> t
    val of_string : string -> t
    val of_out_channel : out_channel -> t
    val output_string : t -> string -> unit
    val output_value : t -> 'a -> unit
  end
    =
  struct
    type t = char -> unit

    let of_buffer (buf:Buffer.t) : t =
      fun (c:char) -> Buffer.add_char buf c

    let of_string (s:string) : t =
      let i = ref 0 in
      fun (c:char) -> s.[!i] <- c  

    let of_out_channel (chan:out_channel) : t =
      fun (c:char) -> output_char chan c

    let output_string (ostream:t) (str:string) =
      String.iter ostream str
   
    let output_value (ostream:t) thing =
      let str = Marshal.to_string thing [] in
      output_string ostream str
     
  end

Maybe it would be prettier to make a matching Istream module,
but I guess it's better to stay with the well-established Stream module.

Issac


>
>
> Thanks,
> Chris
>
> PS.  Please cc me on replies, I temporarily unsubscribed from the 
> list, thanks!
>
> -------------------
> To unsubscribe, mail caml-list-request@inria.fr Archives: 
> http://caml.inria.fr
> Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: 
> http://caml.inria.fr/FAQ/
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
>
>


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Re: [Caml-list] string buffer as (in|out)_channel

[Issac Trotts]

Chris Hecker wrote:

>
> Is there any way to do something similar to the C++ string stream 
> stuff, where you treat strings (or Buffer.t's) as in_ or 
> out_channels?  The Format module has a formatter for strings, but 
> there doesn't seem to be a way to do it with Pervasives.  Something like:
>
> val out_channel_of_buffer : Buffer.t -> out_channel
> val in_channel_of_buffer : Buffer.t -> in_channel
>
> and maybe _of_string versions too (probably necessary because you 
> can't convert a string to a buffer for the in_channel), which fill up 
> and don't expand.
>
> It'd be very useful to be able to do this. 


Please disregard the previous buggy message I sent out.  Here's a 
fixed-up version:

(* read from a Buffer via a Stream *)
let stream_of_buffer buf =
  Stream.from
    (fun i ->
      let s = Buffer.contents buf in
      if i >= String.length s then None else Some s.[i]
    )

(* write to buffers and other things without knowing what they are *)
module Ostream :
  sig
    type t
    val of_function : (char -> unit) -> t
    val of_buffer : Buffer.t -> t
    val of_string : string -> t
    val of_out_channel : out_channel -> t
    val output_char : t -> char -> unit
    val output_string : t -> string -> unit
    val output_value : t -> 'a -> unit
  end
    =
  struct
    type t = char -> unit

    let of_function f = f

    let of_buffer (buf:Buffer.t) : t =
      fun (c:char) -> Buffer.add_char buf c

    let of_string (s:string) : t =
      let i = ref 0 in
      fun (c:char) -> s.[!i] <- c; incr i

    let of_out_channel (chan:out_channel) : t =
      fun (c:char) -> output_char chan c

    let output_char (ostream:t) (c:char) : unit =
      ostream c

    let output_string (ostream:t) (str:string) =
      String.iter ostream str
   
    let output_value (ostream:t) thing =
      let str = Marshal.to_string thing [] in
      output_string ostream str
     
  end


Issac








>
>
> Thanks,
> Chris
>
> PS.  Please cc me on replies, I temporarily unsubscribed from the 
> list, thanks!
>
> -------------------
> To unsubscribe, mail caml-list-request@inria.fr Archives: 
> http://caml.inria.fr
> Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: 
> http://caml.inria.fr/FAQ/
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
>
>


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