[Caml-list] Lwt idioms: iterating

[Caml-list] Lwt idioms: iterating

[Ivan Gotovchits]

What is a best practice to implement a common iterative operations with
Lwt?

For example, I have a data structure incapsulating some
collection. Interface of the structure includes some iterators, i.e.

  val iter (e -> unit) -> t -> unit

  
Now, I would like to output each element of type e using one of the
functions from Lwt_io module. 

I see two solutions and neither I like:

1. Use Buffer.t to accumulate text while iterating, then output it.

2. Use Lwt_stream.t for the same purpose.

Both solutions a rather imperative and too ad-hoc (not scales to other
iterators and tasks). 

Are there any idiomatic solutions for such common tasks in Lwt?

-- 
         (__) 
         (oo) 
   /------\/ 
  / |    ||   
 *  /\---/\ 
    ~~   ~~   
...."Have you mooed today?"...

Re: [Caml-list] Lwt idioms: iterating

[Raphael Proust]

On Wed, Jan 23, 2013 at 5:02 AM, Ivan Gotovchits <ivg@ieee.org> wrote:
>
> What is a best practice to implement a common iterative operations with
> Lwt?
>
> For example, I have a data structure incapsulating some
> collection. Interface of the structure includes some iterators, i.e.
>
>   val iter (e -> unit) -> t -> unit
>
>
> Now, I would like to output each element of type e using one of the
> functions from Lwt_io module.
>
> I see two solutions and neither I like:
>
> 1. Use Buffer.t to accumulate text while iterating, then output it.
>
> 2. Use Lwt_stream.t for the same purpose.

3. Just write it directly and trust the Lwt scheduler to flush the write buffer.

The page https://ocsigen.org/lwt/api/Lwt_io explains that writes are
automatically flushed ``when there is nothing else to do''

~~~~~~~
If you are familiar with buffered channels you may be familiar too
with the flush operation. Note that byte channles of this
modules are automatically flushed when there is nothing else to do
(i.e. before the program goes into idle), so this means that you
no longer have to write:

eprintf "log message\n";
      flush stderr;

to have you messages displayed.
~~~~~~~

>
> Both solutions a rather imperative and too ad-hoc (not scales to other
> iterators and tasks).
>
> Are there any idiomatic solutions for such common tasks in Lwt?
>
> --
>          (__)
>          (oo)
>    /------\/
>   / |    ||
>  *  /\---/\
>     ~~   ~~
> ...."Have you mooed today?"...
>
> --
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-- 
______________
Raphaël Proust