[m-rev.] io__read_file_as_string (was: improve `_init.c' file creation)

[Fergus Henderson]

On 28-Nov-2001, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > > +		% XXX Why does `io__read_file_as_string' return a separate
> > > +		% status and result, rather than an `io__res(string)'?
> > 
> > The reason is to ensure that, in the case when some characters are
> > successfully read and then an I/O error occurs, the part of the file
> > that was successfully read can be returned.
> 
> When is that behaviour useful?

When the error is something such as EINTR.

When implementing programs such as `cat', which should output all that
it successfully reads before reporting a read error.

When the error occurs because the input file is `stdin',
and the user's dialup connection has just been disconnected
due to a Telstra fault.  The data may be hard for the user
to reproduce, so the program should not just throw it away.

> If an error occurs in the middle
> of a read, can the part that was read be trusted?

Yes, to the same degree that any prior successful read can be trusted.

> It also doesn't
> force the user to check for errors before using the result like all
> the other input predicates do (including `io__read_file'). It might be
> better to use a different result type like the one below,

I could live with that.

> but I think
> the best solution is just to return an `io__res(string)' and throw away
> the partially read data.

I couldn't live with that.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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