Re: [Ocaml-lib-devel] Purpose of IO.nread

[Nicolas C. <war...@fr...>]

> > Could you explain how really_input cannot be used on stdin ? Maybe I
> > misunderstood the differences with input, but the documentation doesn't
say
> > anything about really_input not working on stdin.
>
> Apologies - I sent that by accident before I was ready, so it wasn't
> phrased very well.  Of course really_input works on stdin, I was
> thinking of in_channel_length, and IO does wrap that appropriately.
>
> However, the specific case that was giving me problems was using IO as a
> layer for accessing a stream compressed with zlib.  The stream might be
> stdin, so I can't count on knowing how long it is, but for efficiency I
> want to read it in blocks rather than one byte at a time.  In C I'd use
> fread(), in ocaml normally I'd use Pervasives.input.  IO currently
> provides no equivalent.  Sure, it can be done char by char with IO.read,
> but I'm pretty sure that's going to wind up much less efficient than a
> hypothetical function which called Pervasives.input, String.sub, or
> whatever as appropriate.

Sure.
Actually IO does not work maybe well with buffered streams : the
specification is that when you're reading n "elements" (characters or any)
from an input, the result will be exactly the n elements you needed. Not
more, and not less. This might actually be questionable : if you have spare
time, could you suggest what parts of IO module should be modified in order
to support buffered streams ? If it's only replacing
Pervasives.really_input by input (and thus change the specification) I think
it's worth doing.

> I note that this seems to be inconvenient for you, too, going by the
> zlib code you just posted. ;)  Since I want to be able to use data from
> stdin, and I want to be able to handle streams larger than
> Sys.max_string_length, I can't use your version...

This code is still experimental, and will surely be evolve into something
more usable. As for everything else, any suggestion/code contribution will
be apprecied.

Regards,
Nicolas Cannasse