On Wed, Apr 11, 2018 at 12:04 PM, Denis Kudriashov <dionisi...@gmail.com> wrote:
> Hi Alistair.
>
> I don't think anybody is annoyed by you. You are doing really good job. And
> nice thing that you are super patient to continue :)


+100000

>
> What I try to understand is why blocking atEnd is bad?
> Here is code from VMMaker:
>
> [stdin atEnd] whileFalse:
> [| nextChunk |
> stdout nextPutAll: 'squeak> '; flush.
> nextChunk := stdin nextChunkNoTag.
> [nextChunk notEmpty and: [nextChunk first isSeparator]] whileTrue:
> [nextChunk := nextChunk allButFirst].
> Transcript cr; nextPutAll: nextChunk; cr; flush.
> [stdout print: (Compiler evaluate: nextChunk); cr; flush]
> on: Error
> do: [:ex| self logError: ex description inContext: ex signalerContext to:
> stderr]].
> quitOnEof ifTrue:
> [SourceFiles at: 2 put: nil.
> Smalltalk snapshot: false andQuit: true]
>
>
> I am not see why it breaks with blocking #atEnd. Can you explain?
>
> 2018-04-11 11:41 GMT+02:00 Alistair Grant <akgrant0...@gmail.com>:
>>
>> Hi Sven,
>>
>> Oh dear.  I feel as though I'm not getting my concerns across at all
>> well, and I'm pushing hard enough that all I'm going to do is make
>> people annoyed.  So let me try to restate the issue one last time
>> before answering your questions directly.
>>
>> Pharo & Squeak have unwritten rules about stream usage that I suspect
>> have just emerged over time without being designed.
>>
>> If you want to be able to iterate over any stream, and in particular
>> stdin from a terminal (which, as far as I know, is the outlier that
>> causes all the problems) you have to follow these rules:
>>
>> 1.  If the stream is character / byte oriented you have to check for
>> EOF using "stream next == nil".  #atEnd can be used, but you'll still
>> have to do the nil check.
>>
>> 2.  All other streams have to check for EOF (end of stream) using
>> #atEnd.  "stream next == nil" can be used, but you'll still need to
>> test #atEnd to determine whether nil is a value returned by the
>> stream.
>>
>> If you write code that you want to be able to consume characters,
>> bytes or any other object, you'll have to test both "stream next ==
>> nil" and #atEnd.
>>
>> The rules are the result of the original blue book design being that
>> #atEnd should be used, and then character input from a terminal being
>> added later, but always returning an EOF character (nil) before #atEnd
>> answers correctly.
>>
>> At the moment, ZnCharacterEncoder uses #atEnd on character / byte
>> streams, so fails for stdin on a terminal.
>>
>> Back to your questions:
>>
>> On 11 April 2018 at 11:12, Sven Van Caekenberghe <s...@stfx.eu> wrote:
>> >
>> >
>> >> On 11 Apr 2018, at 10:29, Alistair Grant <akgrant0...@gmail.com> wrote:
>> >>
>> >> Hi Denis,
>> >>
>> >> On 11 April 2018 at 10:02, Denis Kudriashov <dionisi...@gmail.com>
>> >> wrote:
>> >>>
>> >>> 2018-04-11 8:32 GMT+02:00 Alistair Grant <akgrant0...@gmail.com>:
>> >>>>
>> >>>>>>> Where is it being said that #next and/or #atEnd should be blocking
>> >>>>>>> or
>> >>>>>>> non-blocking ?
>> >>>>>>
>> >>>>>> There is existing code that assumes that #atEnd is non-blocking and
>> >>>>>> that #next is allowed block.  I believe that we should keep those
>> >>>>>> conditions.
>> >>>>>
>> >>>>> I fail to see where that is written down, either way. Can you point
>> >>>>> me
>> >>>>> to comments stating that, I would really like to know ?
>> >>>>
>> >>>> I'm not aware of it being written down, just that ever existing
>> >>>> implementation I'm aware of behaves this way.
>> >>>>
>> >>>> On the other hand, making #atEnd blocking breaks Eliot's REPL sample
>> >>>> (in Squeak).
>> >>>
>> >>>
>> >>> Could you write here this example, please?
>> >>
>> >> The code is loaded in squeak using:
>> >>
>> >>
>> >> https://github.com/OpenSmalltalk/opensmalltalk-vm/blob/Cog/image/buildspurtrunkreaderimage.sh
>> >>
>> >> for 32 bit images.  It loads:
>> >>
>> >>
>> >> https://github.com/OpenSmalltalk/opensmalltalk-vm/blob/Cog/image/LoadReader.st
>> >>
>> >> which loads package CogTools-Listener in
>> >> http://source.squeak.org/VMMaker
>> >>
>> >> An image that automatically runs the code and nothing else is created
>> >> in:
>> >>
>> >>
>> >> https://github.com/OpenSmalltalk/opensmalltalk-vm/blob/Cog/image/StartReader.st
>> >>
>> >>
>> >> If you want to run it interactively you can load CogTools-Listener and
>> >> do something like:
>> >>
>> >> StdioListener new
>> >>    quitOnEof: false;
>> >>    run
>> >
>> > What does #quitOnEof: do ? Can the StdioListener code be browsed/viewed
>> > online somewhere ?
>>
>> I just referenced this as an example of making #atEnd (really
>> FilePlugin>>primitiveFileAtEnd) blocking causing problems.  I wasn't
>> expecting people to go and look at the code or use it as a test.
>>
>> If you really want to look at it (from Pharo):
>>
>> 1. Add http://source.squeak.org/VMMaker as a repository.
>> 2. Browse the CogTools-Listener package
>>
>>
>> >> If you modify #atEnd to block it will result in the "squeak>" input
>> >> prompt being printed in the terminal after the input has been entered.
>> >
>> > How does one modify #atEnd to block ? I suppose you are talking about
>> > StdioStream>>#atEnd ?
>>
>> I meant the primitive, i.e. FilePlugin>>primitiveFileAtEnd /
>> FilePluginPrims>>atEnd:.
>>
>>
>> >  ^ self peek isNil
>> >
>> > ?
>> >
>> > PS: I liked your runnable example better, I will try it later on. Thx!
>>
>> Right.  My code is meant to be minimal and trigger the problem I'm
>> actually focused on - that ZnCharacterEncoder doesn't work with stdin
>> from a terminal.
>>
>> Sven has expressed a hesitation to change the internal operation of
>> the Zinc streams from using #atEnd to "stream peek == nil" and this
>> whole discussion is really about us trying to resolve our different
>> perspective of the best path forward.  I respect Sven and his work so
>> I'm trying to justify the change (but I'm not expressing it at all
>> well, obviously).
>>
>> Cheers,
>> Alistair
>>
>>
>>
>> >> The code can be loaded in to Pharo and basically works, but the output
>> >> tends to be hidden behind the next input prompt because it uses #cr
>> >> instead of #lf.  You can easily modify StdioListener>>initialize to
>> >> set the line end convention in stdout.
>> >>
>> >> NOTE: It is not intended to be a release quality implementation of a
>> >> evaluation loop.  The whole purpose as I understand it is for it to be
>> >> as simple as possible to assist in tracking down issues using the VM
>> >> simulator.  It runs minimal code to get to the point of waiting for
>> >> user input and then allows an expression that causes problems to be
>> >> entered and traced using the simulator.
>> >>
>> >> Cheers,
>> >> Alistair
>> >>
>> >>
>> >>
>> >>>>>>> How is this related to how EOF is signalled ?
>> >>>>>>
>> >>>>>> Because, combined with terminal EOF not being known until the user
>> >>>>>> explicitly flags it (with Ctrl-D) it means that #atEnd can't be
>> >>>>>> used
>> >>>>>> for iterating over input from stdin connected to a terminal.
>> >>>>>
>> >>>>> This seems to me like an exception that only holds for one
>> >>>>> particular
>> >>>>> stream in one particular scenario (interactive stdin). I might be
>> >>>>> wrong.
>> >>>>>
>> >>>>>>> It seems to me that there are quite a few classes of streams that
>> >>>>>>> are
>> >>>>>>> 'special' in the sense that #next could be blocking and/or #atEnd
>> >>>>>>> could be
>> >>>>>>> unclear - socket/network streams, serial streams, maybe stdio
>> >>>>>>> (interactive
>> >>>>>>> or not). Without a message like #isDataAvailable you cannot handle
>> >>>>>>> those
>> >>>>>>> without blocking.
>> >>>>>>
>> >>>>>> Right.  I think this is a distraction (I was trying to explain some
>> >>>>>> details, but it's causing more confusion instead of helping).
>> >>>>>>
>> >>>>>> The important point is that #atEnd doesn't work for iterating over
>> >>>>>> streams with terminal input
>> >>>>>
>> >>>>> Maybe you should also point to the actual code that fails. I mean
>> >>>>> you
>> >>>>> showed a partial stack trace, but not how you got there, precisely.
>> >>>>> How does
>> >>>>> the application reading from an interactive stdin do to get into
>> >>>>> trouble ?
>> >>>>
>> >>>> Included below.
>> >>>>
>> >>>>
>> >>>>>>> Reading from stdin seems like a very rare case for a Smalltalk
>> >>>>>>> system
>> >>>>>>> (not that it should not be possible).
>> >>>>>>
>> >>>>>> There's been quite a bit of discussion and several projects
>> >>>>>> recently
>> >>>>>> related to using pharo for scripting, so it may become more common.
>> >>>>>> E.g.
>> >>>>>>
>> >>>>>>
>> >>>>>>
>> >>>>>> https://www.quora.com/Can-Smalltalk-be-a-batch-file-scripting-language/answer/Philippe-Back-1?share=c19bfc95
>> >>>>>> https://github.com/rajula96reddy/pharo-cli
>> >>>>>
>> >>>>> Still, it is not common at all.
>> >>>>>
>> >>>>>>> I have a feeling that too much functionality is being pushed into
>> >>>>>>> too
>> >>>>>>> small an API.
>> >>>>>>
>> >>>>>> This is just about how should Zinc streams be iterating over the
>> >>>>>> underlying streams.  You didn't like checking the result of #next
>> >>>>>> for
>> >>>>>> nil since it isn't general, correctly pointing out that nil is a
>> >>>>>> valid
>> >>>>>> value for non-byte oriented streams.  But #atEnd doesn't work for
>> >>>>>> stdin from a terminal.
>> >>>>>>
>> >>>>>>
>> >>>>>> At this point I think there are three options:
>> >>>>>>
>> >>>>>> 1. Modify Zinc to check the return value of #next instead of using
>> >>>>>> #atEnd.
>> >>>>>>
>> >>>>>> This is what all existing character / byte oriented streams in
>> >>>>>> Squeak
>> >>>>>> and Pharo do.  At that point the Zinc streams can be used on all
>> >>>>>> file
>> >>>>>> / stdio input and output.
>> >>>>>
>> >>>>> I agree that such code exists in many places, but there is lots of
>> >>>>> stream reading that does not check for nils.
>> >>>>
>> >>>> Right.  Streams can be categorised in many ways, but for this
>> >>>> discussion I think streams are broken in to two types:
>> >>>>
>> >>>> 1) Byte / Character oriented
>> >>>> 2) All others
>> >>>>
>> >>>> For historical reasons, byte / character oriented streams need to
>> >>>> check for EOF by using "stream next == nil" and all other streams
>> >>>> should use #atEnd.
>> >>>>
>> >>>> This avoids the "nil being part of the domain" issue that was
>> >>>> discussed earlier in the thread.
>> >>>>
>> >>>>
>> >>>>>> 2. Modify all streams to signal EOF in some other way, i.e. a
>> >>>>>> sentinel
>> >>>>>> or notification / exception.
>> >>>>>>
>> >>>>>> This is what we were discussing below.  But it is a decent chunk of
>> >>>>>> work with significant impact on the existing code base.
>> >>>>>
>> >>>>> Agreed. This would be a future extension.
>> >>>>>
>> >>>>>> 3. Require anyone who wants to read from stdin to code around
>> >>>>>> Zinc's
>> >>>>>> inability to handle terminal input.
>> >>>>>>
>> >>>>>> I'd prefer to avoid this option if possible.
>> >>>>>
>> >>>>> See higher for a more concrete usage example request.
>> >>>>
>> >>>>
>> >>>> testAtEnd.st
>> >>>> --
>> >>>> | ch stream string stdin |
>> >>>>
>> >>>> 'stdio.cs' asFileReference fileIn.
>> >>>> "stdin := FileStream stdin."
>> >>>> stdin := ZnCharacterReadStream on:
>> >>>>    (ZnBufferedReadStream on:
>> >>>>        Stdio stdin).
>> >>>> stream := (String new: 100) writeStream.
>> >>>> ch := stdin next.
>> >>>> [ ch == nil ] whileFalse: [
>> >>>>    stream nextPut: ch.
>> >>>>    ch := stdin next. ].
>> >>>> string := stream contents.
>> >>>> FileStream stdout
>> >>>>    nextPutAll: string; lf;
>> >>>>    nextPutAll: 'Characters read: ';
>> >>>>    nextPutAll: string size asString;
>> >>>>    lf.
>> >>>> Smalltalk snapshot: false andQuit: true.
>> >>>> --
>> >>>>
>> >>>> Execute with:
>> >>>>
>> >>>> ./pharo --headless Pharo7.0-64bit-e76f1a2.image testAtEnd.st
>> >>>>
>> >>>> and type Ctrl-D gives:
>> >>>>
>> >>>>
>> >>>> 'Errors in script loaded from testAtEnd.st'
>> >>>> MessageNotUnderstood: receiver of "<" is nil
>> >>>> UndefinedObject(Object)>>doesNotUnderstand: #<
>> >>>> ZnUTF8Encoder>>nextCodePointFromStream:
>> >>>> ZnUTF8Encoder(ZnCharacterEncoder)>>nextFromStream:
>> >>>> ZnCharacterReadStream>>nextElement
>> >>>> ZnCharacterReadStream(ZnEncodedReadStream)>>next
>> >>>> UndefinedObject>>DoIt
>> >>>> OpalCompiler>>evaluate
>> >>>>
>> >>>>
>> >>>> Using #atEnd to control the loop instead of "stdin next == nil"
>> >>>> produces the same result.
>> >>>>
>> >>>> Replacing stdin with FileStream stdin makes the script work.
>> >>>>
>> >>>> stdio.cs fixes a bug in StdioStream which really isn't part of this
>> >>>> discussion (PR to be submitted).
>> >>>>
>> >>>> Cheers,
>> >>>> Alistair
>> >>>>
>> >>>>
>> >>>>
>> >>>>
>> >>>>>> Does that clarify the situation?
>> >>>>>
>> >>>>> Yes, it helps. Thanks. But questions remain.
>> >>>>>
>> >>>>>> Thanks,
>> >>>>>> Alistair
>> >>>>>>
>> >>>>>>
>> >>>>>>
>> >>>>>>>> On 10 Apr 2018, at 18:30, Alistair Grant <akgrant0...@gmail.com>
>> >>>>>>>> wrote:
>> >>>>>>>>
>> >>>>>>>> First a quick update:
>> >>>>>>>>
>> >>>>>>>> After doing some work on primitiveFileAtEnd, #atEnd now answers
>> >>>>>>>> correctly for files that don't report their size correctly, e.g.
>> >>>>>>>> /dev/urandom and /proc/cpuinfo, whether the files are opened
>> >>>>>>>> directly
>> >>>>>>>> or
>> >>>>>>>> redirected through stdin.
>> >>>>>>>>
>> >>>>>>>> However determining whether stdin from a terminal has reached the
>> >>>>>>>> end
>> >>>>>>>> of
>> >>>>>>>> file can't be done without making #atEnd blocking since we have
>> >>>>>>>> to
>> >>>>>>>> wait
>> >>>>>>>> for the user to flag the end of file, e.g. by typing Ctrl-D.  And
>> >>>>>>>> #atEnd
>> >>>>>>>> is assumed to be non-blocking.
>> >>>>>>>>
>> >>>>>>>> So currently using ZnCharacterReadStream with stdin from a
>> >>>>>>>> terminal
>> >>>>>>>> will
>> >>>>>>>> result in a stack dump similar to:
>> >>>>>>>>
>> >>>>>>>> MessageNotUnderstood: receiver of "<" is nil
>> >>>>>>>> UndefinedObject(Object)>>doesNotUnderstand: #<
>> >>>>>>>> ZnUTF8Encoder>>nextCodePointFromStream:
>> >>>>>>>> ZnUTF8Encoder(ZnCharacterEncoder)>>nextFromStream:
>> >>>>>>>> ZnCharacterReadStream>>nextElement
>> >>>>>>>> ZnCharacterReadStream(ZnEncodedReadStream)>>next
>> >>>>>>>> UndefinedObject>>DoIt
>> >>>>>>>>
>> >>>>>>>>
>> >>>>>>>> Going back through the various suggestions that have been made
>> >>>>>>>> regarding
>> >>>>>>>> using a sentinel object vs. raising a notification / exception,
>> >>>>>>>> my
>> >>>>>>>> (still to be polished) suggestion is to:
>> >>>>>>>>
>> >>>>>>>> 1. Add an endOfStream instance variable
>> >>>>>>>> 2. When the end of the stream is reached answer the value of the
>> >>>>>>>> instance variable (i.e. the result of sending #value to the
>> >>>>>>>> variable).
>> >>>>>>>> 3. The initial default value would be a block that raises a
>> >>>>>>>> Deprecation
>> >>>>>>>> warning and then returns nil.  This would allow existing code to
>> >>>>>>>> function for a changeover period.
>> >>>>>>>> 4. At the end of the deprecation period the default value would
>> >>>>>>>> be
>> >>>>>>>> changed to a unique sentinel object which would answer itself as
>> >>>>>>>> its
>> >>>>>>>> #value.
>> >>>>>>>>
>> >>>>>>>> At any time users of the stream can set their own sentinel,
>> >>>>>>>> including
>> >>>>>>>> a
>> >>>>>>>> block that raises an exception.
>> >>>>>>>>
>> >>>>>>>>
>> >>>>>>>> Cheers,
>> >>>>>>>> Alistair
>> >>>>>>>>
>> >>>>>>>>
>> >>>>>>>> On 4 April 2018 at 19:24, Stephane Ducasse
>> >>>>>>>> <stepharo.s...@gmail.com>
>> >>>>>>>> wrote:
>> >>>>>>>>> Thanks for this discussion.
>> >>>>>>>>>
>> >>>>>>>>> On Wed, Apr 4, 2018 at 1:37 PM, Sven Van Caekenberghe
>> >>>>>>>>> <s...@stfx.eu>
>> >>>>>>>>> wrote:
>> >>>>>>>>>> Alistair,
>> >>>>>>>>>>
>> >>>>>>>>>> First off, thanks for the discussions and your contributions, I
>> >>>>>>>>>> really appreciate them.
>> >>>>>>>>>>
>> >>>>>>>>>> But I want to have a discussion at the high level of the
>> >>>>>>>>>> definition
>> >>>>>>>>>> and semantics of the stream API in Pharo.
>> >>>>>>>>>>
>> >>>>>>>>>>> On 4 Apr 2018, at 13:20, Alistair Grant
>> >>>>>>>>>>> <akgrant0...@gmail.com>
>> >>>>>>>>>>> wrote:
>> >>>>>>>>>>>
>> >>>>>>>>>>> On 4 April 2018 at 12:56, Sven Van Caekenberghe <s...@stfx.eu>
>> >>>>>>>>>>> wrote:
>> >>>>>>>>>>>> Playing a bit devil's advocate, the idea is that, in general,
>> >>>>>>>>>>>>
>> >>>>>>>>>>>> [ stream atEnd] whileFalse: [ stream next. "..." ].
>> >>>>>>>>>>>>
>> >>>>>>>>>>>> is no longer allowed ?
>> >>>>>>>>>>>
>> >>>>>>>>>>> It hasn't been allowed "forever" [1].  It's just been misused
>> >>>>>>>>>>> for
>> >>>>>>>>>>> almost as long.
>> >>>>>>>>>>>
>> >>>>>>>>>>> [1] Time began when stdio stream support was introduced. :-)
>> >>>>>>>>>>
>> >>>>>>>>>> I am still not convinced. Another way to put it would be that
>> >>>>>>>>>> the
>> >>>>>>>>>> old #atEnd or #upToEnd do not make sense for these streams and
>> >>>>>>>>>> some new loop
>> >>>>>>>>>> is needed, based on a new test (it exists for socket streams
>> >>>>>>>>>> already).
>> >>>>>>>>>>
>> >>>>>>>>>> [ stream isDataAvailable ] whileTrue: [ stream next ]
>> >>>>>>>>>>
>> >>>>>>>>>>>> And you want to replace it with
>> >>>>>>>>>>>>
>> >>>>>>>>>>>> [ stream next ifNil: [ false ] ifNotNil: [ :x | "..." true ]
>> >>>>>>>>>>>> whileTrue.
>> >>>>>>>>>>>>
>> >>>>>>>>>>>> That is a pretty big change, no ?
>> >>>>>>>>>>>
>> >>>>>>>>>>> That's the way quite a bit of code already operates.
>> >>>>>>>>>>>
>> >>>>>>>>>>> As Denis pointed out, it's obviously problematic in the
>> >>>>>>>>>>> general
>> >>>>>>>>>>> sense,
>> >>>>>>>>>>> since nil can be embedded in non-byte oriented streams.  I
>> >>>>>>>>>>> suspect
>> >>>>>>>>>>> that in practice not many people write code that reads streams
>> >>>>>>>>>>> from
>> >>>>>>>>>>> both byte oriented and non-byte oriented streams.
>> >>>>>>>>>>
>> >>>>>>>>>> Maybe yes, maybe no. As Denis' example shows there is a clear
>> >>>>>>>>>> definition problem.
>> >>>>>>>>>>
>> >>>>>>>>>> And I do use streams of byte arrays or strings all the time,
>> >>>>>>>>>> this
>> >>>>>>>>>> is really important. I want my parsers to work on all kinds of
>> >>>>>>>>>> streams.
>> >>>>>>>>>>
>> >>>>>>>>>>>> I think/feel like a proper EOF exception would be better,
>> >>>>>>>>>>>> more
>> >>>>>>>>>>>> correct.
>> >>>>>>>>>>>>
>> >>>>>>>>>>>> [ [ stream next. "..." true ] on: EOF do: [ false ] ]
>> >>>>>>>>>>>> whileTrue.
>> >>>>>>>>>>>
>> >>>>>>>>>>> I agree, but the email thread Nicolas pointed to raises some
>> >>>>>>>>>>> performance questions about this approach.  It should be
>> >>>>>>>>>>> straightforward to do a basic performance comparison which
>> >>>>>>>>>>> I'll
>> >>>>>>>>>>> get
>> >>>>>>>>>>> around to if other objections aren't raised.
>> >>>>>>>>>>
>> >>>>>>>>>> Reading in bigger blocks, using #readInto:startingAt:count:
>> >>>>>>>>>> (which
>> >>>>>>>>>> is basically Unix's (2) Read sys call), would solve performance
>> >>>>>>>>>> problems, I
>> >>>>>>>>>> think.
>> >>>>>>>>>>
>> >>>>>>>>>>>> Will we throw away #atEnd then ? Do we need it if we cannot
>> >>>>>>>>>>>> use
>> >>>>>>>>>>>> it ?
>> >>>>>>>>>>>
>> >>>>>>>>>>> Unix file i/o returns EOF if the end of file has been reach OR
>> >>>>>>>>>>> if
>> >>>>>>>>>>> an
>> >>>>>>>>>>> error occurs.  You should still check #atEnd after reading
>> >>>>>>>>>>> past
>> >>>>>>>>>>> the
>> >>>>>>>>>>> end of the file to make sure no error occurred.  Another part
>> >>>>>>>>>>> of
>> >>>>>>>>>>> the
>> >>>>>>>>>>> primitive change I'm proposing is to return additional
>> >>>>>>>>>>> information
>> >>>>>>>>>>> about what went wrong in the event of an error.
>> >>>>>>>>>>
>> >>>>>>>>>> I am sorry, but this kind of semantics (the OR) is way too
>> >>>>>>>>>> complex
>> >>>>>>>>>> at the general image level, it is too specific and based on
>> >>>>>>>>>> certain
>> >>>>>>>>>> underlying implementation details.
>> >>>>>>>>>>
>> >>>>>>>>>> Sven
>> >>>>>>>>>>
>> >>>>>>>>>>> We could modify the read primitive so that it fails if an
>> >>>>>>>>>>> error
>> >>>>>>>>>>> has
>> >>>>>>>>>>> occurred, and then #atEnd wouldn't be required.
>> >>>>>>>>>>>
>> >>>>>>>>>>> Cheers,
>> >>>>>>>>>>> Alistair
>> >>>>>>>>>>>
>> >>>>>>>>>>>
>> >>>>>>>>>>>
>> >>>>>>>>>>>>> On 4 Apr 2018, at 12:41, Alistair Grant
>> >>>>>>>>>>>>> <akgrant0...@gmail.com>
>> >>>>>>>>>>>>> wrote:
>> >>>>>>>>>>>>>
>> >>>>>>>>>>>>> Hi Nicolas,
>> >>>>>>>>>>>>>
>> >>>>>>>>>>>>> On 4 April 2018 at 12:36, Nicolas Cellier
>> >>>>>>>>>>>>> <nicolas.cellier.aka.n...@gmail.com> wrote:
>> >>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>
>> >>>>>>>>>>>>>> 2018-04-04 12:18 GMT+02:00 Alistair Grant
>> >>>>>>>>>>>>>> <akgrant0...@gmail.com>:
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> Hi Sven,
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> On Wed, Apr 04, 2018 at 11:32:02AM +0200, Sven Van
>> >>>>>>>>>>>>>>> Caekenberghe wrote:
>> >>>>>>>>>>>>>>>> Somehow, somewhere there was a change to the
>> >>>>>>>>>>>>>>>> implementation
>> >>>>>>>>>>>>>>>> of the
>> >>>>>>>>>>>>>>>> primitive called by some streams' #atEnd.
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> That's a proposed change by me, but it hasn't been
>> >>>>>>>>>>>>>>> integrated
>> >>>>>>>>>>>>>>> yet.  So
>> >>>>>>>>>>>>>>> the discussion below should apply to the current stable vm
>> >>>>>>>>>>>>>>> (from August
>> >>>>>>>>>>>>>>> last year).
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> IIRC, someone said it is implemented as 'remaining size
>> >>>>>>>>>>>>>>>> being
>> >>>>>>>>>>>>>>>> zero'
>> >>>>>>>>>>>>>>>> and some virtual unix files like /dev/random are zero
>> >>>>>>>>>>>>>>>> sized.
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> Currently, for files other than sdio (stdout, stderr,
>> >>>>>>>>>>>>>>> stdin)
>> >>>>>>>>>>>>>>> it is
>> >>>>>>>>>>>>>>> effectively defined as:
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> atEnd := stream position >= stream size
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> And, as you say, plenty of virtual unix files report size
>> >>>>>>>>>>>>>>> 0.
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> Now, all kinds of changes are being done image size to
>> >>>>>>>>>>>>>>>> work
>> >>>>>>>>>>>>>>>> around this.
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> I would phrase this slightly differently :-)
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> Some code does the right thing, while other code doesn't.
>> >>>>>>>>>>>>>>> E.g.:
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> MultiByteFileStream>>upToEnd is good, while
>> >>>>>>>>>>>>>>> FileStream>>contents is incorrect
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> I am a strong believer in simple, real (i.e. infinite)
>> >>>>>>>>>>>>>>>> streams, but I
>> >>>>>>>>>>>>>>>> am not sure we are doing the right thing here.
>> >>>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> Point is, I am not sure #next returning nil is official
>> >>>>>>>>>>>>>>>> and
>> >>>>>>>>>>>>>>>> universal.
>> >>>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> Consider the comments:
>> >>>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> Stream>>#next
>> >>>>>>>>>>>>>>>> "Answer the next object accessible by the receiver."
>> >>>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> ReadStream>>#next
>> >>>>>>>>>>>>>>>> "Primitive. Answer the next object in the Stream
>> >>>>>>>>>>>>>>>> represented
>> >>>>>>>>>>>>>>>> by the
>> >>>>>>>>>>>>>>>> receiver. Fail if the collection of this stream is not an
>> >>>>>>>>>>>>>>>> Array or a
>> >>>>>>>>>>>>>>>> String.
>> >>>>>>>>>>>>>>>> Fail if the stream is positioned at its end, or if the
>> >>>>>>>>>>>>>>>> position is out
>> >>>>>>>>>>>>>>>> of
>> >>>>>>>>>>>>>>>> bounds in the collection. Optional. See Object
>> >>>>>>>>>>>>>>>> documentation
>> >>>>>>>>>>>>>>>> whatIsAPrimitive."
>> >>>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> Note how there is no talk about returning nil !
>> >>>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> I think we should discuss about this first.
>> >>>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> Was the low level change really correct and the right
>> >>>>>>>>>>>>>>>> thing
>> >>>>>>>>>>>>>>>> to do ?
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> The primitive change proposed doesn't affect this
>> >>>>>>>>>>>>>>> discussion.
>> >>>>>>>>>>>>>>> It will
>> >>>>>>>>>>>>>>> mean that #atEnd returns false (correctly) sometimes,
>> >>>>>>>>>>>>>>> while
>> >>>>>>>>>>>>>>> currently it
>> >>>>>>>>>>>>>>> returns true (incorrectly).  The end result is still
>> >>>>>>>>>>>>>>> incorrect, e.g.
>> >>>>>>>>>>>>>>> #contents returns an empty string for /proc/cpuinfo.
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> You're correct about no mention of nil, but we have:
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> FileStream>>next
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>    (position >= readLimit and: [self atEnd])
>> >>>>>>>>>>>>>>>            ifTrue: [^nil]
>> >>>>>>>>>>>>>>>            ifFalse: [^collection at: (position := position
>> >>>>>>>>>>>>>>> +
>> >>>>>>>>>>>>>>> 1)]
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> which has been around for a long time (I suspect, before
>> >>>>>>>>>>>>>>> Pharo
>> >>>>>>>>>>>>>>> existed).
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> Having said that, I think that raising an exception is a
>> >>>>>>>>>>>>>>> better
>> >>>>>>>>>>>>>>> solution, but it is a much, much bigger change than the
>> >>>>>>>>>>>>>>> one I
>> >>>>>>>>>>>>>>> proposed
>> >>>>>>>>>>>>>>> in https://github.com/pharo-project/pharo/pull/1180.
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>> Cheers,
>> >>>>>>>>>>>>>>> Alistair
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>
>> >>>>>>>>>>>>>> Hi,
>> >>>>>>>>>>>>>> yes, if you are after universal behavior englobing Unix
>> >>>>>>>>>>>>>> streams, the
>> >>>>>>>>>>>>>> Exception might be the best way.
>> >>>>>>>>>>>>>> Because on special stream you can't allways say in advance,
>> >>>>>>>>>>>>>> you
>> >>>>>>>>>>>>>> have to try.
>> >>>>>>>>>>>>>> That's the solution adopted by authors of Xtreams.
>> >>>>>>>>>>>>>> But there is a runtime penalty associated to it.
>> >>>>>>>>>>>>>>
>> >>>>>>>>>>>>>> The penalty once was so high that my proposal to generalize
>> >>>>>>>>>>>>>> EndOfStream
>> >>>>>>>>>>>>>> usage was rejected a few years ago by AndreaRaab.
>> >>>>>>>>>>>>>> http://forum.world.st/EndOfStream-unused-td68806.html
>> >>>>>>>>>>>>>
>> >>>>>>>>>>>>> Thanks for this, I'll definitely take a look.
>> >>>>>>>>>>>>>
>> >>>>>>>>>>>>> Do you have a sense of how Denis' suggestion of using an
>> >>>>>>>>>>>>> EndOfStream
>> >>>>>>>>>>>>> object would compare?
>> >>>>>>>>>>>>>
>> >>>>>>>>>>>>> It would keep the same coding style, but avoid the problems
>> >>>>>>>>>>>>> with
>> >>>>>>>>>>>>> nil.
>> >>>>>>>>>>>>>
>> >>>>>>>>>>>>> Thanks,
>> >>>>>>>>>>>>> Alistair
>> >>>>>>>>>>>>>
>> >>>>>>>>>>>>>
>> >>>>>>>>>>>>>
>> >>>>>>>>>>>>>> I have regularly benched Xtreams, but stopped a few years
>> >>>>>>>>>>>>>> ago.
>> >>>>>>>>>>>>>> Maybe i can excavate and pass on newer VM.
>> >>>>>>>>>>>>>>
>> >>>>>>>>>>>>>> In the mean time, i had experimented a programmable end of
>> >>>>>>>>>>>>>> stream behavior
>> >>>>>>>>>>>>>> (via a block, or any other valuable)
>> >>>>>>>>>>>>>> http://www.squeaksource.com/XTream.htm
>> >>>>>>>>>>>>>> so as to reconcile performance and universality, but it was
>> >>>>>>>>>>>>>> a
>> >>>>>>>>>>>>>> source of
>> >>>>>>>>>>>>>> complexification at implementation side.
>> >>>>>>>>>>>>>>
>> >>>>>>>>>>>>>> Nicolas
>> >>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> Note also that a Guille introduced something new, #closed
>> >>>>>>>>>>>>>>>> which is
>> >>>>>>>>>>>>>>>> related to the difference between having no more elements
>> >>>>>>>>>>>>>>>> (maybe right now,
>> >>>>>>>>>>>>>>>> like an open network stream) and never ever being able to
>> >>>>>>>>>>>>>>>> produce more data.
>> >>>>>>>>>>>>>>>>
>> >>>>>>>>>>>>>>>> Sven
>> >>>>>>>>>>>>
>> >>>>>>>>>>>>
>> >>>>>>>>>>>
>> >>>>>>>>>>
>> >>>>>>>>>>
>> >>>>>>>>>
>> >>>>>>>>
>> >>>>>>>
>> >>>>>>>
>> >>>>>> <stdio.cs>
>> >
>> >
>>
>

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