An approach I like is to add an endOfStreamValue inst var to Stream and answer its value when at end.  This way nil does not have to be the endOfStreamValue, for example -1 might be much more convenient for a binary stream, and streams can answer nil without confusing their clients.  atEnd can be implemented as
    atEnd
        ^self peek = self endOfStreamValue

You can arrange to make streams raise an end-of-stream exception instead of the endOfStreamValue by using some convention on the contents of endOfStreamValue, such as if it is == to the stream itself (although I note that in the Teleplace image the exception EndOfStrean is defined bit not used).


Of course, stream primitives get in the way of adding inst vars to stream classes ;)

IMO this is a much more useful scheme than making nil the only endOfStream value.

On Fri, Nov 27, 2009 at 2:33 PM, Eliot Miranda <eliot.miranda@gmail.com> wrote:


On Fri, Nov 27, 2009 at 2:24 PM, Nicolas Cellier <nicolas.cellier.aka.nice@gmail.com> wrote:
2009/11/27 Colin Putney <cputney@wiresong.ca>:
>
> On 27-Nov-09, at 8:03 AM, David T. Lewis wrote:
>
>> I implemented IOHandle for this, see http://wiki.squeak.org/squeak/996.
>> I have not maintained it since about 2003, but the idea is
>> straightforward.
>
> Yes. I looked into IOHandle when implementing Filesystem, but decided to go
> with a new (simpler, but limited) implementation that would let me explore
> the requirements for the stream architecture I had in mind.
>
>> My purpose at that time was to :
>>
>>  * Separate the representation of external IO channels from the
>> represention
>>   of streams and communication protocols.
>>  * Provide a uniform representation of IO channels similar to the unix
>> notion
>>   of treating everything as a 'file'.
>>  * Simplify future refactoring of Socket and FileStream.
>>  * Provide a place for handling asynchronous IO events. Refer to the aio
>>   handling in the unix VM. Files, Sockets, and AsyncFiles could (should)
>> use
>>   a common IO event handling mechanism (aio event signaling a Smalltalk
>> Semaphore).
>
> Indeed. Filesystem comes at this from the other direction, but I think we
> want to end up in the same place. For now I've done TSTTCPW, which is use
> the primitives from the FilePlugin. But eventually I want to improve the
> plumbing. You've done some important work here - perhaps Filesystem can use
> AioPlugin at some point.
>
> Colin
>
>

I wonder why level 3 stdio was used (FILE * fopen, fclose ...) rather
than level 2 (int fid, open, close, ...) in file plugin... Better
portability ?

level 2 isn't really a level, its a section of the unix manual pages.  Section 2 is the system calls (which really define what unix is).  Section 3 is libraries.  So only the stdio library in section 3 is portable across C implementations.  So yes, you're right, the use of the C library's stdio facilities was chosen for portability.

Nicolas