Re: [9fans] rc's shortcomings (new subject line)

Re: [9fans] rc's shortcomings (new subject line)

[Lucio De Re]

> Errr ... no. Twice: mash was not VN code but brucee's preemptive strike
> against a POSIX shell for Lucent's Inferno;
> VN's Inferno had a shell with a different style done by Roger Peppe.

I do apologise.  Mash was genial!  The VN shell was remarkable in a
very different way.

++L

Re: [9fans] rc's shortcomings (new subject line)

[😜]

Hi, just my 2¢ for the fanning out of pipes: if I remember correctly,
mycroftiv's hubfs (or some other software in his contrib) allowed one to
do exactly this.
hth

On 08/28/2012 09:41 PM, Dan Cross wrote:
> On Tue, Aug 28, 2012 at 8:56 PM, erik quanstrom <quanstro@quanstro.net> wrote:
>>> And rc is not perfect.  I've always felt like the 'if not' stuff was a kludge.
>>
>> no, it's certainly not.  (i wouldn't call if not a kludge—just ugly.
> 
> Kludge perhaps in the sense that it seems to be to work around an
> issue with the grammar and the expectation that it's mostly going to
> be used interactively, as opposed to programmatically.  See below.
> 
>> the haahr/rakitzis es' if makes more sense, even if it's wierder.)
> 
> Agreed; es would be an interesting starting point for a new shell.
> 
>> but the real question with rc is, what would you fix?
> 
> I think in order to really answer that question, one would have to
> step back for a moment and really think about what one wants out of a
> shell.  There seems to be a natural conflict a programming language
> and a command interpreter (e.g., the 'if' vs. 'if not' thing).  On
> which side does one err?
> 
>> i can only think of a few things around the edges.  `{} and $ are
>> obvious and is some way to use standard regular expressions.  but
>> those really aren't that motivating.  rc does enough.
> 
> I tend to agree.  As a command interpreter, rc is more or less fine as
> is.  I'd really only feel motivated to change whatever people felt
> were common nits, and there are fairly few of those.
> 
>> perhaps (let's hope) someone else has better ideas.
> 
> Well, something off the top of my head: Unix pipelines are sort of
> like chains of coroutines.  And they work great for defining linear
> combinations of filters.  But something that may be interesting would
> be the ability to allow the stream of computations to branch; instead
> of pipelines being just a list, make them a tree, or even some kind of
> dag (if one allows for the possibility of recombining streams).  That
> would be kind of an interesting thing to play with in a shell
> language; I don't know how practically useful it would be, though.
> 
>>> switch/case would make helluva difference over nested if/if not, if
>>> defaulted to fall-through.
>>
>> maybe you have an example?  because i don't see that.  if not works
>> fine, and can be nested.  case without fallthrough is also generally
>> what i want.  if not, i can make the common stuff a function.
>>
>>> variable scoping (better than subshel) would help writing larger
>>> scripts, but that's not necessarily an improvement ;-) something
>>> similar to LISP's `let' special form, for dynamic binding.
> 
> (A nit: 'let' actually introduces lexical scoping in most Lisp
> variants; yes, doing (let ((a 1)) ...) has non-lexical effect if 'a'
> is a dynamic variable in Common Lisp, but (let) doesn't itself
> introduce dynamic variables.  Emacs Lisp is a notable exception in
> this regard.)
> 
>> there is variable scoping.  you can write
>>
>>         x=() y=() cmd
>>
>> cmd can be a function body or whatever.  x and y are then private
>> to cmd.  you can nest redefinitions.
>>
>>         x=1 y=2 {echo first $x $y; x=a y=b {echo second $x $y; x=α y=β {echo third $x $y}; echo ret second $x $y}; echo ret first $x $y}
>>         first 1 2
>>         second a b
>>         third α β
>>         ret second a b
>>         ret first 1 2
> 
> This syntax feels clunky and unfamiliar to me; rc resembles block
> scoped languages like C; I'd rather have a 'local' or similar keyword
> to introduce a variable in the scope of each '{ }' block.
> 
>> you should try the es shell.  es had let and some other scheme-y
>> features.  let allows one to do all kinds of tricky stuff, like build
>> a shell debugger in the shell, but my opinion is that es was more
>> powerful and fun, but it didn't buy enough because it didn't really
>> expand on the essential nature of a shell.  what can one do to
>> manipulate processes and file descriptors.
> 
> es was a weird merger between rc's syntax and functional programming
> concepts.  It's neat-ish, but unless we're really ready to go to the
> pipe monad (not that weird, in my opinion) you're right.  Still, if it
> allowed one to lexically bind a file descriptor to a variable, I could
> see that being neat; could I have a closure over a file descriptor?  I
> don't think the underlying process model is really set up for it, but
> it would be kind of cool: one could have different commands consuming
> part of a stream in a very flexible way.
> 
>         - Dan C.
> 

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

On Thu Aug 30 10:56:52 EDT 2012, charles.forsyth@gmail.com wrote:

> As another example, also from Flex,
> J M Foster, I F Currie, "Remote Capabilities", The Computer Journal, 30(5),
> 1987, pp. 451-7.
>
> http://comjnl.oxfordjournals.org/content/30/5/451.full.pdf

very intersting.  the paper says that although capabilities
are enforced by microcode, and therefore can be proven,
it would be possible to build the system from cots parts.
so i'm wondering if kernel participation is necessary?

- erik

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

On Thu Aug 30 16:08:23 EDT 2012, charles.forsyth@gmail.com wrote:

> That's true, but the C compiler also does each .c in parallel up to NPROC.
> 
> On 30 August 2012 18:18, erik quanstrom <quanstro@labs.coraid.com> wrote:
> 
> > > Even more common than reduce is map. No reason why you can't
> > > parallelize
> > >
> > >       8c *.c
> >
> > we already do—with mk.

ha!  i hadn't seen that before.  too bad mk doesn't (generally) use it.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[Charles Forsyth]

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That's true, but the C compiler also does each .c in parallel up to NPROC.

On 30 August 2012 18:18, erik quanstrom <quanstro@labs.coraid.com> wrote:

> > Even more common than reduce is map. No reason why you can't
> > parallelize
> >
> >       8c *.c
>
> we already do—with mk.
>

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Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> Even more common than reduce is map. No reason why you can't
> parallelize
> 
> 	8c *.c

we already do—with mk.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[Bakul Shah]

On Thu, 30 Aug 2012 15:35:47 +0530 Dan Cross <crossd@gmail.com>  wrote:
> On Wed, Aug 29, 2012 at 7:27 PM, erik quanstrom <quanstro@quanstro.net> wrote
> :
> >> > rc already has non-linear pipelines.  but they're not very convienient.
> >>
> >> And somewhat limited.  There's no real concept of 'fanout' of output,
> >> for instance (though that's a fairly trivial command, so probably
> >> doesn't count), or multiplexing input from various sources that would
> >> be needed to implement something like a shell-level data flow network.
> >>
> >> Muxing input from multiple sources is hard when the data isn't somehow
> >> self-delimited.
> >>[...]
> >> There may be other ways to achieve the same thing; I remember that the
> >> boundaries of individual writes used to be preserved on read, but I
> >> think that behavior changed somewhere along the way; maybe with the
> >> move away from streams?  Or perhaps I'm misremembering?
> >
> > pipes still preserve write boundaries, as does il.  (even the 0-byte write)
>  but tcp of course by
> > definition does not.  but either way, the protocol would need to be
> > self-framed to be transported on tcp.  and even then, there are protocols
> > that are essentially serial, like tls.
>
> Right.  I think this is the reason for Bakul's question about
> s-expressions or JSON or a similar format; those formats are
> inherently self-delimiting.

Indeed.

>                              The problem with that is that, for
> passing those things around to work without some kind of reverse
> 'tee'-like intermediary, the system has to understand the the things
> that are being transferred are s-expressions or JSON records or
> whatever, not just streams of uninterpreted bytes.  We've steadfastly
> rejected such system-imposing structure on files in Unix-y type
> environments since 1969.

I think that it is time to try something new.  A lot of things
don't fit into into this model of bytepipes connecting
processes. A lot of commands even in this model use line
"objects". But the kind of composability one gets in Scheme,
go, functional languages etc is missing. Even go seems to go
the "one language for all" Lispy model -- its typed channels
are all within a single address space. [Actually I would have
much preferred if they had just focused on adding channels and
parallel processes to a Scheme instead of creating a whole new
language but that is whole 'nother discussion!]

> But conceptually, these IPC mechanisms are sort of similar to channels
> in CSP-style languages.  A natural question then becomes, how do
> CSP-style languages handle the issue?  Channels work around the muxing
> thing by being typed; elements placed onto a channel are indivisible
> objects of that type, so one doesn't need to worry about interference
> from other objects simultaneously placed onto the same channel in
> other threads of execution.  Could we do something similar with pipes?
>  I don't know that anyone wants typed file descriptors; that would
> open a whole new can of worms.

I am suggesting channels of self-typed objects.  The idea of
communicating self-identifying objects between loosely coupled
processes is blindingly obvious to me. And as long as you have
one producer/one consumer pair, there are no problems in
implementing this on any system but the unix model of
"inheriting" file descriptors (or even passing them around to
unrelated processes) and then letting them all blab
indiscriminately on the same channel just doesn't work. So again
Unix gets in the way.

> This sounds wonderful, of course, but in Lisp and Scheme, lists are
> built from cons cells, and even if I have some magic
> 'split-into-halves' function that satisfies the requirements of
> reduce, doing so is still necessarily linear, so I don't gain much.
> Besides, having to pass around the identity all the time is a bummer.

You can use cdr-coding. Or just use arrays like APL/j/k. But a
knowledge of function properties is essential to implement
them efficiently and for one arg version (without the initial
value). In k "/" is the reduce operator so you can say

    +/!3	// !3 == 0 1 2
    0+/!3 	// two arg version of +.

And
    */!0
    +/!0
do the right thing because the language knows identity
elements for + and *.

> But in clojure, the Lisp concept of a list (composed of cons cells) is
> generalized into the concept of a 'seq'.  A seq is just a sequence of
> things; it could be a list, a vector, some other container (say, a
> sequence of key/value pairs derived from some kind of associated
> structure), or a stream of data being read from a file or network
> connection.
>
> What's the *real* problem here?  The issue is that reduce "knows" too
> much about the things it is reducing over.  Doing things sequentially
> is easy, but slow; doing things in parallel requires that reduce know
> a lot about the type of thing it's reducing over (e.g., this magic
> 'split-into-halves' function.  Further, that might not be appropriate
> for *all* sequence types; e.g., files or lists made from cons cells.

Even more common than reduce is map. No reason why you can't
parallelize

	8c *.c

> Your example of running multiple 'grep's in parallel sort of reminded
> me of this, though it occurs to me that this can probably be done with

This is a map not reduce. The "reduce" would be implicitly
(and often wrongly) done by fd inheritance.

I have a toy array-scheme where all functions except array
functions are applied elementwise when given arrays.

	(+ #(1 2 3) #(4 5 6)) => #(5 7 9)
	(* 2 #(4 5 6)) => #(8 10 12)
	(* 2 #(4 #(5 5) 6)) => #(8 #(10 10) 12)

So I think map can be made implicit but reduction has to be
explicit. This is what APLs do.

> a command: a sort of 'parallel apply' thing that can run a command
> multiple times concurrently, each invocation on a range of the
> arguments.  But making it simple and elegant is likely to be tricky.

APL/k have peach for parallel-each ("each" is their way of saying map).

Re: [9fans] rc's shortcomings (new subject line)

[Charles Forsyth]

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The source of mash as VN inherited it from the defunct Lucent organisation
on 1 September 1999 remains in the tree,
so it wasn't lost.

On 30 August 2012 16:13, Charles Forsyth <charles.forsyth@gmail.com> wrote:
>
> On 30 August 2012 16:13, Lucio De Re <lucio@proxima.alt.za> wrote:
>
>> Inferno (Vitanuova) released a "mash" a ways back, but apparently the
>> sources were lost.
>>
>
>

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Re: [9fans] rc's shortcomings (new subject line)

[Charles Forsyth]

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Errr ... no. Twice: mash was not VN code but brucee's preemptive strike
against a POSIX shell for Lucent's Inferno;
VN's Inferno had a shell with a different style done by Roger Peppe.

On 30 August 2012 16:13, Lucio De Re <lucio@proxima.alt.za> wrote:

> Inferno (Vitanuova) released a "mash" a ways back, but apparently the
> sources were lost.
>

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Re: [9fans] rc's shortcomings (new subject line)

[Lucio De Re]

> anyway, a meld of Rc shell and mk? crazy idea.

Inferno (Vitanuova) released a "mash" a ways back, but apparently the
sources were lost.  It was mind-bogglingly interesting!

++L

Re: [9fans] rc's shortcomings (new subject line)

[sl]

> anyway, a meld of Rc shell and mk? crazy idea.

What was mash?

-sl

Re: [9fans] rc's shortcomings (new subject line)

[Burton Samograd]

>> anyway, a meld of Rc shell and mk? crazy idea.

> Inferno (Vitanuova) released a "mash" a ways back, but apparently the sources were lost.  It was mind-bogglingly interesting!

In case anyone's interested (like I was):

http://www.vitanuova.com/inferno/man/1/mash.html

--
Burton Samograd

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Re: [9fans] rc's shortcomings (new subject line)

[Charles Forsyth]

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As another example, also from Flex,
J M Foster, I F Currie, "Remote Capabilities", The Computer Journal, 30(5),
1987, pp. 451-7.

http://comjnl.oxfordjournals.org/content/30/5/451.full.pdf

On 30 August 2012 15:45, Charles Forsyth <charles.forsyth@gmail.com> wrote:

> If you look at the paper I referenced, you will. Similar abilities
> appeared in systems that supported persistence and persistent programming
> languages (cf. Malcolm Atkinson, not Wikipedia).

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Re: [9fans] rc's shortcomings (new subject line)

[dexen deVries]

On Thursday 30 of August 2012 10:41:38 erik quanstrom wrote: 
> what i was saying is that mk knows and insures that the output files
> are there.  the fact that it's not in the middle of the conversation is
> an implementation detail, imho.
> 
> that is, mk is built on the assumption that programs communicate through
> files; $O^c communicates to $O^l by producing .$O files.  mk rules
> know this.

shouldn't be the case for rules with virtual targets (V). such rules are 
always executed, and the order should only depend on implementatino of DAG 
traversing. ``Files may be made in any order that respects the preceding 
restrictions'', from manpage.

if mk was used for executing grep in parallel, prerequisites would be actual 
files, but targets would be virtual; probably 1...$NPROC targets per 
directory.


anyway, a meld of Rc shell and mk? crazy idea.


-- 
dexen deVries

[[[↓][→]]]

I'm sorry that this was such a long lett­er, but I didn't have time to write 
you a short one. -- Bla­ise Pasc­al

Re: [9fans] rc's shortcomings (new subject line)

[Charles Forsyth]

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If you look at the paper I referenced, you will. Similar abilities appeared
in systems that supported persistence and persistent programming
languages (cf. Malcolm Atkinson, not Wikipedia).

On 30 August 2012 14:33, erik quanstrom <quanstro@quanstro.net> wrote:

> i don't see that the os can really help here.

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Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

On Thu Aug 30 10:28:24 EDT 2012, crossd@gmail.com wrote:
> > said another way, we already have typed streams, but they're not
> > enforced by the operating system.
>
> Yes, but then every program that participates in one of these
> computation networks has to have that type knowledge baked in.  The
> Plan 9/Unix model seems to preclude a general mechanism.

that's what i thought when i first read the plan 9 papers.  but it
turns out, that it works out just fine for file servers, ssl, authentication,
etc.  why can't it work for another type of agreed protocol?  obviously
you'd need something along the lines of tlsclient/tlssrv if you wanted
normal programs to do this, but it might be that just a subset of programs
are really interested in participating.

> > one can also use the thread library technique, using shared memory.
>
> Sure, but that doesn't do much for designing a new shell.  :-)

the shell itself could have channels, without the idea escaping
into the wild.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> On Thu, Aug 30, 2012 at 7:56 PM, erik quanstrom <quanstro@quanstro.net> wrote:
> >> The thing is that mk doesn't really do anything to set up connections
> >> between the commands it runs.
> >
> > it does.  the connections are through the file system.
>
> No.  The order in which commands are run (or if they are run at all)
> is based on file timestamps, so in that sense it uses the filesystem
> for coordination, but mk itself doesn't do anything to facilitate
> interprocess communications between the commands it runs (for example
> setting up pipes between commands).

what i was saying is that mk knows and insures that the output files
are there.  the fact that it's not in the middle of the conversation is
an implementation detail, imho.

that is, mk is built on the assumption that programs communicate through
files; $O^c communicates to $O^l by producing .$O files.  mk rules
know this.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> Hmm, I'm afraid I'm off in the realm of thinking out loud at this
> point.  Sorry if that's noisy for folks.

THANK YOU.  if 9fans needs anything, it's more thinking.

i'm not an edison fan, but i do like one thing he said, which was
that he had not failed, but simply discovered that the $n ways
he'd tried so far do not work.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[Dan Cross]

On Thu, Aug 30, 2012 at 7:56 PM, erik quanstrom <quanstro@quanstro.net> wrote:
>> The thing is that mk doesn't really do anything to set up connections
>> between the commands it runs.
>
> it does.  the connections are through the file system.

No.  The order in which commands are run (or if they are run at all)
is based on file timestamps, so in that sense it uses the filesystem
for coordination, but mk itself doesn't do anything to facilitate
interprocess communications between the commands it runs (for example
setting up pipes between commands).

        - Dan C.

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> > grep -b.  but in general if the bio library had an option to output
> > line-wise, then the problem could be avoided.  otherwise, one would need to
> > mux the output.
>
>
> to quote you, erik,
> > pipes still preserve write boundaries, as does il
>
> so, hopefully, a dumb pipe to cat would do the job...? :^)
>
> grep-single-directory:VQ: $FILES_IN_THE_DIR
> 	grep $regex $prereq | cat

i think you still need grep -b, because otherwise grep uses
the bio library to buffer output, and bio doesn't respect lines.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> The thing is that mk doesn't really do anything to set up connections
> between the commands it runs.

it does.  the connections are through the file system.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[dexen deVries]

On Thursday 30 of August 2012 09:47:59 you wrote:
> > caveat: output of one grep instance could end up in the midst of a /line/
> > of output of another grep instance.
> 
> grep -b.  but in general if the bio library had an option to output
> line-wise, then the problem could be avoided.  otherwise, one would need to
> mux the output.


to quote you, erik,
> pipes still preserve write boundaries, as does il

so, hopefully, a dumb pipe to cat would do the job...? :^)

grep-single-directory:VQ: $FILES_IN_THE_DIR
	grep $regex $prereq | cat


-- 
dexen deVries

[[[↓][→]]]

I'm sorry that this was such a long lett­er, but I didn't have time to write 
you a short one. -- Bla­ise Pasc­al

Re: [9fans] rc's shortcomings (new subject line)

[Dan Cross]

On Thu, Aug 30, 2012 at 7:51 PM, Dan Cross <crossd@gmail.com> wrote:
> A parallel apply sort of thing could be used with xargs, of course;
> 'whatever | xargs papply foo' could keep some $n$ of foo's running at
> the same time.  The magic behind 'papply foo `{whatever}' is that it
> knows how to interpret its arguments in blocks.  xargs will invoke a
> command after reading $n$ arguments, but that's mainly to keep from
> overflowing the argument buffer, and (to my knowledge) it won't try to
> keep multiple instances running them in parallel.

Oops, I should have checked the man page before I wrote.  It seems
that at least some version of xargs have a '-P' for 'parallel' mode.

Re: [9fans] rc's shortcomings (new subject line)

[Dan Cross]

On Thu, Aug 30, 2012 at 7:11 PM, dexen deVries <dexen.devries@gmail.com> wrote:
> On Thursday 30 of August 2012 15:35:47 Dan Cross wrote:
>> (...)
>> Your example of running multiple 'grep's in parallel sort of reminded
>> me of this, though it occurs to me that this can probably be done with
>> a command: a sort of 'parallel apply' thing that can run a command
>> multiple times concurrently, each invocation on a range of the
>> arguments.  But making it simple and elegant is likely to be tricky.
>
> now that i think of it...
>
> mk creates DAG of dependences and then reduces it by calling commands, going
> in parallel where applicable.
>
> erik's example with grep x *.[ch] boils down to two cases:
>  - for single use, do it simple & slow way -- just run single grep process for
> all files
>  - but when you expect to traverse those files often, prepare a mkfile
> (preferably in a semi-automatic way) which will perform search in parallel.
>
> caveat: output of one grep instance could end up in the midst of a /line/ of
> output of another grep instance.

The thing is that mk doesn't really do anything to set up connections
between the commands it runs.

Re: [9fans] rc's shortcomings (new subject line)

[Dan Cross]

On Thu, Aug 30, 2012 at 7:03 PM, erik quanstrom <quanstro@quanstro.net> wrote:
>> rejected such system-imposing structure on files in Unix-y type
>> environments since 1969.
> [...]
>> other threads of execution.  Could we do something similar with pipes?
>>  I don't know that anyone wants typed file descriptors; that would
>> open a whole new can of worms.
>
> i don't see that the os can really help here.  lib9p has no problem
> turning an undelimited byte stream → 9p messages.  there's no reason
> any other format couldn't get the same treatment.

Yeah, I don't see much here unless one breaks the untyped stream model
(from the perspective of the system).

> said another way, we already have typed streams, but they're not
> enforced by the operating system.

Yes, but then every program that participates in one of these
computation networks has to have that type knowledge baked in.  The
Plan 9/Unix model seems to preclude a general mechanism.

> one can also use the thread library technique, using shared memory.

Sure, but that doesn't do much for designing a new shell.  :-)

>> Consider a simple reduction in Lisp; say, summing up a list of numbers
>> or something like that.  In Common Lisp, we may write this as:
>>
>>     (reduce #'+ '(1 2 3 4 5))
>>
>> In clojure, the same thing would be written as:
>>
>>     (reduce + [1 2 3 4 5])
>>
>
> this reminds me of a bit of /bin/man.  it seemed that the case statement
> to generate a pipeline of formatting commands was awkward—verbose
> and yet limited.
>
>         fn pipeline{
>                 if(~ $#* 0)
>                         troff $Nflag $Lflag -$MAN | $postproc
>                 if not{
>                         p = $1; shift
>                         $p | pipeline $*
>                 }
>         }
>
>         fn roff {
>                 ...
>                 fontdoc $2 | pipeline $preproc
>         }

Ha!  That's something.  I'm not sure what, but definitely something (I
actually kind of like it).

>> http://clojure.com/blog/2012/05/08/reducers-a-library-and-model-for-collection-processing.html
>>
>> Your example of running multiple 'grep's in parallel sort of reminded
>> me of this, though it occurs to me that this can probably be done with
>> a command: a sort of 'parallel apply' thing that can run a command
>> multiple times concurrently, each invocation on a range of the
>> arguments.  But making it simple and elegant is likely to be tricky.
>
> actually, unless i misread (i need more coffee), the blog sounds just like
> xargs.

Hmm, not exactly.  xargs would be like reducers if xargs somehow asked
stdin to apply a program to itself.

A parallel apply sort of thing could be used with xargs, of course;
'whatever | xargs papply foo' could keep some $n$ of foo's running at
the same time.  The magic behind 'papply foo `{whatever}' is that it
knows how to interpret its arguments in blocks.  xargs will invoke a
command after reading $n$ arguments, but that's mainly to keep from
overflowing the argument buffer, and (to my knowledge) it won't try to
keep multiple instances running them in parallel.

Hmm, I'm afraid I'm off in the realm of thinking out loud at this
point.  Sorry if that's noisy for folks.

        - Dan C.

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> caveat: output of one grep instance could end up in the midst of a /line/ of
> output of another grep instance.

grep -b.  but in general if the bio library had an option to output line-wise,
then the problem could be avoided.  otherwise, one would need to mux the
output.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[dexen deVries]

On Thursday 30 of August 2012 15:35:47 Dan Cross wrote:
> (...)
> Your example of running multiple 'grep's in parallel sort of reminded
> me of this, though it occurs to me that this can probably be done with
> a command: a sort of 'parallel apply' thing that can run a command
> multiple times concurrently, each invocation on a range of the
> arguments.  But making it simple and elegant is likely to be tricky.

now that i think of it...

mk creates DAG of dependences and then reduces it by calling commands, going 
in parallel where applicable.

erik's example with grep x *.[ch] boils down to two cases:
 - for single use, do it simple & slow way -- just run single grep process for 
all files
 - but when you expect to traverse those files often, prepare a mkfile 
(preferably in a semi-automatic way) which will perform search in parallel.

caveat: output of one grep instance could end up in the midst of a /line/ of 
output of another grep instance.



-- 
dexen deVries

[[[↓][→]]]

I'm sorry that this was such a long lett­er, but I didn't have time to write 
you a short one. -- Bla­ise Pasc­al

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> rejected such system-imposing structure on files in Unix-y type
> environments since 1969.
[...]
> other threads of execution.  Could we do something similar with pipes?
>  I don't know that anyone wants typed file descriptors; that would
> open a whole new can of worms.

i don't see that the os can really help here.  lib9p has no problem
turning an undelimited byte stream → 9p messages.  there's no reason
any other format couldn't get the same treatment.

said another way, we already have typed streams, but they're not
enforced by the operating system.

one can also use the thread library technique, using shared memory.

> Consider a simple reduction in Lisp; say, summing up a list of numbers
> or something like that.  In Common Lisp, we may write this as:
> 
>     (reduce #'+ '(1 2 3 4 5))
> 
> In clojure, the same thing would be written as:
> 
>     (reduce + [1 2 3 4 5])
> 

this reminds me of a bit of /bin/man.  it seemed that the case statement
to generate a pipeline of formatting commands was awkward—verbose
and yet limited.

	fn pipeline{
		if(~ $#* 0)
			troff $Nflag $Lflag -$MAN | $postproc
		if not{
			p = $1; shift
			$p | pipeline $*
		}
	}

	fn roff {
		...
		fontdoc $2 | pipeline $preproc
	}

> http://clojure.com/blog/2012/05/08/reducers-a-library-and-model-for-collection-processing.html
> 
> Your example of running multiple 'grep's in parallel sort of reminded
> me of this, though it occurs to me that this can probably be done with
> a command: a sort of 'parallel apply' thing that can run a command
> multiple times concurrently, each invocation on a range of the
> arguments.  But making it simple and elegant is likely to be tricky.

actually, unless i misread (i need more coffee), the blog sounds just like
xargs.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[Charles Forsyth]

[-- Attachment #1: Type: text/plain, Size: 155 bytes --]

typed command languages:
I F Currie, J M Foster, Curt: The Command Interpreter Language for Flex
  http://www.vitanuova.com/dist/doc/rsre-3522-curt.pdf

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Re: [9fans] rc's shortcomings (new subject line)

[Dan Cross]

On Wed, Aug 29, 2012 at 7:27 PM, erik quanstrom <quanstro@quanstro.net> wrote:
>> > rc already has non-linear pipelines.  but they're not very convienient.
>>
>> And somewhat limited.  There's no real concept of 'fanout' of output,
>> for instance (though that's a fairly trivial command, so probably
>> doesn't count), or multiplexing input from various sources that would
>> be needed to implement something like a shell-level data flow network.
>>
>> Muxing input from multiple sources is hard when the data isn't somehow
>> self-delimited.
>>[...]
>> There may be other ways to achieve the same thing; I remember that the
>> boundaries of individual writes used to be preserved on read, but I
>> think that behavior changed somewhere along the way; maybe with the
>> move away from streams?  Or perhaps I'm misremembering?
>
> pipes still preserve write boundaries, as does il.  (even the 0-byte write) but tcp of course by
> definition does not.  but either way, the protocol would need to be
> self-framed to be transported on tcp.  and even then, there are protocols
> that are essentially serial, like tls.

Right.  I think this is the reason for Bakul's question about
s-expressions or JSON or a similar format; those formats are
inherently self-delimiting.  The problem with that is that, for
passing those things around to work without some kind of reverse
'tee'-like intermediary, the system has to understand the the things
that are being transferred are s-expressions or JSON records or
whatever, not just streams of uninterpreted bytes.  We've steadfastly
rejected such system-imposing structure on files in Unix-y type
environments since 1969.

But conceptually, these IPC mechanisms are sort of similar to channels
in CSP-style languages.  A natural question then becomes, how do
CSP-style languages handle the issue?  Channels work around the muxing
thing by being typed; elements placed onto a channel are indivisible
objects of that type, so one doesn't need to worry about interference
from other objects simultaneously placed onto the same channel in
other threads of execution.  Could we do something similar with pipes?
 I don't know that anyone wants typed file descriptors; that would
open a whole new can of worms.

Maybe the building blocks are all there; one could imagine some kind
of 'splitter' program that could take input and rebroadcast it across
multiple output descriptors.  Coupled with some kind of 'merge'
program that could take multiple input streams and mux them onto a
single output, one could build nearly arbitrarily complicated networks
of computations connected by pipes.  Maybe for simplicity constrain
these to be DAGs.  With a notation to describe these computation
graphs, one could just do a topological sort of the graph, create
pipes in all the appropriate places and go from there.  Is the shell
an appropriate place for such a thing?

Forsyth's link looks interesting; I haven't read through the paper in
detail yet, but it sort of reminded me of LabView in a way (where
non-programmers wire together data flows using boxes and arrows and
stuff).

>> > i suppose i'm stepping close to sawzall now.
>>
>> Actually, I think you're stepping closer to the reducers stuff Rich
>> Hickey has done recently in Clojure, though there's admittedly a lot
>> of overlap with the sawzall way of looking at things.
>
> my knowledge of both is weak.  :-)

The Clojure reducers stuff is kind of slick.

Consider a simple reduction in Lisp; say, summing up a list of numbers
or something like that.  In Common Lisp, we may write this as:

    (reduce #'+ '(1 2 3 4 5))

In clojure, the same thing would be written as:

    (reduce + [1 2 3 4 5])

The problem is how the computation is performed.  To illustrate,
here's a simple definition of 'reduce' written in Scheme (R5RS doesn't
have a standard 'reduce' function, but it is most commonly written to
take an initial element, so I do that here).

    (define (reduce binop a bs)
      (if (null? bs)
        a
        (reduce binop (binop a (car bs)) (cdr bs))))

Notice how the recursive depth of the function is linear in the length
of the list.  But, if one thinks about what I'm doing here (just
addition of simple numbers) there's no reason this can't be done in
parallel.  In particular, if I can split the list into evenly sized
parts and recurse, I can limit the recursive depth of the computation
to O(lg n).  Something more like:

    (define (reduce binop a bs)
      (if (null? bs)
        a
        (let ((halves (split-into-halves bs)))
          (binop (reduce binop a (car halves)) (reduce binop a (cadr halves)))

If I can exploit parallelism to execute functions in the recursion
tree simultaneously, I can really cut down on execution time.  The
requirement is that binop over a and bs's is a monoid; that is, binop
is associative over the set from which 'a' and 'bs' are drawn, and 'a'
is an identity element.

This sounds wonderful, of course, but in Lisp and Scheme, lists are
built from cons cells, and even if I have some magic
'split-into-halves' function that satisfies the requirements of
reduce, doing so is still necessarily linear, so I don't gain much.
Besides, having to pass around the identity all the time is a bummer.

But in clojure, the Lisp concept of a list (composed of cons cells) is
generalized into the concept of a 'seq'.  A seq is just a sequence of
things; it could be a list, a vector, some other container (say, a
sequence of key/value pairs derived from some kind of associated
structure), or a stream of data being read from a file or network
connection.

What's the *real* problem here?  The issue is that reduce "knows" too
much about the things it is reducing over.  Doing things sequentially
is easy, but slow; doing things in parallel requires that reduce know
a lot about the type of thing it's reducing over (e.g., this magic
'split-into-halves' function.  Further, that might not be appropriate
for *all* sequence types; e.g., files or lists made from cons cells.

The insight of the reducers framework is that one can just ask the
container to reduce itself.  Basically, pass it a function and say,
"here, reduce yourself with this function however you see fit."  Then,
random-access containers can do things in parallel; lists and files
and things can do things sequentially; associative containers can do
whatever they want, etc.  The implementation is kind of interesting;
more information is here:
http://clojure.com/blog/2012/05/08/reducers-a-library-and-model-for-collection-processing.html

Your example of running multiple 'grep's in parallel sort of reminded
me of this, though it occurs to me that this can probably be done with
a command: a sort of 'parallel apply' thing that can run a command
multiple times concurrently, each invocation on a range of the
arguments.  But making it simple and elegant is likely to be tricky.

        - Dan C.

Re: [9fans] rc's shortcomings (new subject line)

[Charles Forsyth]

[-- Attachment #1: Type: text/plain, Size: 532 bytes --]

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.78.5331
Paul Haeberli, ConMan: A Visual Programming Language for Interactive
Graphics (1988)
I supervised a student who did an implementation for a Blit-like
environment on the Sun3 as a project;
unfortunately I didn't keep a copy. I remember there were several things
left to work out based on the paper.
(The Blit-like environment replaced megabytes of Sunview, in case you were
wondering, and enabled some serious fun.
Sunview enabled some serious head-banging.)

[-- Attachment #2: Type: text/html, Size: 867 bytes --]

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> > rc already has non-linear pipelines.  but they're not very convienient.
>
> And somewhat limited.  There's no real concept of 'fanout' of output,
> for instance (though that's a fairly trivial command, so probably
> doesn't count), or multiplexing input from various sources that would
> be needed to implement something like a shell-level data flow network.
>
> Muxing input from multiple sources is hard when the data isn't somehow
> self-delimited.
>[...]
> There may be other ways to achieve the same thing; I remember that the
> boundaries of individual writes used to be preserved on read, but I
> think that behavior changed somewhere along the way; maybe with the
> move away from streams?  Or perhaps I'm misremembering?

pipes still preserve write boundaries, as does il.  (even the 0-byte write) but tcp of course by
definition does not.  but either way, the protocol would need to be
self-framed to be transported on tcp.  and even then, there are protocols
that are essentially serial, like tls.

> > i suppose i'm stepping close to sawzall now.
>
> Actually, I think you're stepping closer to the reducers stuff Rich
> Hickey has done recently in Clojure, though there's admittedly a lot
> of overlap with the sawzall way of looking at things.

my knowledge of both is weak.  :-)

- erik

Re: [9fans] rc's shortcomings (new subject line)

[Dan Cross]

On Wed, Aug 29, 2012 at 2:04 AM, erik quanstrom <quanstro@quanstro.net> wrote:
>> > the haahr/rakitzis es' if makes more sense, even if it's wierder.)
>>
>> Agreed; es would be an interesting starting point for a new shell.
>
> es is great input.  there are really cool ideas there, but it does
> seem like a lesson learned to me, rather than a starting point.

Starting point conceptually, if not in implementation.

>> I think in order to really answer that question, one would have to
>> step back for a moment and really think about what one wants out of a
>> shell.  There seems to be a natural conflict a programming language
>> and a command interpreter (e.g., the 'if' vs. 'if not' thing).  On
>> which side does one err?
>
> since the raison d'être of a shell is to be a command interpter, i'd
> go with that.

Fair enough, but that will color the flavor of the shell when used as
a programming language.  Then again, Inferno's shell was able to
successfully navigate both in a comfortable manner by using clever
facilities available in that environment (module loading and the
like).  It's not clear how well that works in an environment like
Unix, let alone Plan 9.

>> I tend to agree.  As a command interpreter, rc is more or less fine as
>> is.  I'd really only feel motivated to change whatever people felt
>> were common nits, and there are fairly few of those.
>
> there are nits of omission, and those can be fixable.  ($x(n-m) was added)

Right.

>> > perhaps (let's hope) someone else has better ideas.
>>
>> Well, something off the top of my head: Unix pipelines are sort of
>> like chains of coroutines.  And they work great for defining linear
>> combinations of filters.  But something that may be interesting would
>> be the ability to allow the stream of computations to branch; instead
>> of pipelines being just a list, make them a tree, or even some kind of
>> dag (if one allows for the possibility of recombining streams).  That
>> would be kind of an interesting thing to play with in a shell
>> language; I don't know how practically useful it would be, though.
>
> rc already has non-linear pipelines.  but they're not very convienient.

And somewhat limited.  There's no real concept of 'fanout' of output,
for instance (though that's a fairly trivial command, so probably
doesn't count), or multiplexing input from various sources that would
be needed to implement something like a shell-level data flow network.

Muxing input from multiple sources is hard when the data isn't somehow
self-delimited.  For specific applications this is solvable by the
various pieces of the computation just agreeing on how to represent
data and having a program that takes that into account do the muxing,
but for a general mechanism it's much more difficult, and the whole
self-delimiting thing breaks the Unix 'data as text' abstraction by
imposing a more rigid structure.

There may be other ways to achieve the same thing; I remember that the
boundaries of individual writes used to be preserved on read, but I
think that behavior changed somewhere along the way; maybe with the
move away from streams?  Or perhaps I'm misremembering?  I do remember
that it led to all sorts of hilarious arguments about what the
behavior of things like, 'write(fd, "", 0)' should induce in the
reading side of things, but this was a long time ago.

Anyway, maybe something along the lines of, 'read a message of length
<=SOME_MAX_SIZE from a file descriptor; the message boundaries are
determined by the sending end and preserved by read/write' could be
leveraged here without too much disruption to the current model.

> i think part of the problem is answering the question, what problem
> would we like to solve.  because "a better shell" just isn't well-defined
> enough.

Agreed.

> my knee-jerk reaction to my own question is that making it easier
> and more natural to parallelize dataflow.  a pipeline is just a really
> low-level way to talk about it.  the standard
>         grep x *.[ch]
> forces all the *.[ch] to be generated before 1 instance of grep runs on
> whatever *.[ch] evaluates to be.
>
> but it would be okay for almost every use of this if *.[ch] were generated
> in parallel with any number of grep's being run.
>
> i suppose i'm stepping close to sawzall now.

Actually, I think you're stepping closer to the reducers stuff Rich
Hickey has done recently in Clojure, though there's admittedly a lot
of overlap with the sawzall way of looking at things.

        - Dan C.

Re: [9fans] rc's shortcomings (new subject line)

[dexen deVries]

On Wednesday 29 of August 2012 09:06:35 arisawa wrote:
> Hello,
> 
> On 2012/08/29, at 4:34, dexen deVries wrote:
> > now i see i can do:
> > 
> > x=1 y=2 z=3
> > 
> > ...and only `z' retains its new value in the external scope, while `x' and
> > `y' are limited in scope.
> 
> No.
> 
> ar% a=1 b=2 c=3; echo $a $b $c
> 1 2 3
> ar% a=() b=() c=()
> ar% a=1 b=2 {c=3}; echo $a $b $c
> 3
> ar%


indeed, thanks.


-- 
dexen deVries

[[[↓][→]]]

I'm sorry that this was such a long lett­er, but I didn't have time to write 
you a short one. -- Bla­ise Pasc­al

Re: [9fans] rc's shortcomings (new subject line)

[dexen deVries]

On Tuesday 28 of August 2012 16:34:10 erik quanstrom wrote:
> my knee-jerk reaction to my own question is that making it easier
> and more natural to parallelize dataflow.  a pipeline is just a really
> low-level way to talk about it.  the standard
> 	grep x *.[ch]
> forces all the *.[ch] to be generated before 1 instance of grep runs on
> whatever *.[ch] evaluates to be.
> 
> but it would be okay for almost every use of this if *.[ch] were generated
> in parallel with any number of grep's being run.


(in Linux terms, sorry!)

you can get close with find|xargs -- it runs the command for every -L <number> 
lines of input. AFAIK xargs does not parallelize the execution itself.


find -name '*.[ch]' | xargs -L 8 grep REGEX


-- 
dexen deVries

[[[↓][→]]]

I'm sorry that this was such a long lett­er, but I didn't have time to write 
you a short one. -- Bla­ise Pasc­al

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> > > > > The feature I want is the ability to pass not just character
> > > > > values in environment or pipes but arbitrary Scheme objects.
> > > > > But that requires changes at the OS level (or mapping them
> > > > > to/from strings, which is a waste if both sides can handle
> > > > > structured objects).
> > > >
> > > > !?  the ability to pass typed records around is an idea that was
> > > > tarred, feathered, drawn and quartered by unix.  files, and therefore
> > > > streams, have no type.  they are byte streams.
> > >
> > > I was not talking about "records" but s-expressions.  "json"
> > > is kind of sort of the same thing. Without a generally useful
> > > and simple such mechanism, people end up devising their own.
> > > The 9p format for instance. And go has typed channels.
> >
> > it sounds like you're saying 9p isn't useful.  .... i must be reading
> > your post incorrectly.
>
> 9p is quite useful. But the same semantics could've been
> implemented using a more universal but compact structured
> format such as s-expr. It is not the only choice but to me it
> seems to strike a reasonable balance (compared to bloaty XML
> at one extreme, tightly packed binary structures at another,
> and byte streams with printf/parse encode/decode at the third
> extreme).

i don't see the problem.  9p is not in any way special to the kernel.
only devmnt knows about it, and it is only used to mount file servers.
in theory, one could substitue something else.  it wouldn't quite be
plan 9, and it wouldn't be interoperable, but there's no reason it couldn't
be done.  authentication speaks special protocols.  venti speaks a special
protocol.  so i don't see why kernel support would even be helpful in
implementing your s-expression protocol.  and there's no reason
a 9p over s-expression device can't be implemented.

imho, the reason for constraining 9p to exactly the operations needed
is to make it easy to prove the protocol correct.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[Bakul Shah]

On Tue, 28 Aug 2012 22:23:20 EDT erik quanstrom <quanstro@quanstro.net>  wrote:
> > On Tue, 28 Aug 2012 21:39:06 EDT erik quanstrom <quanstro@quanstro.net>  wr
> ote:
> > > > The feature I want is the ability to pass not just character
> > > > values in environment or pipes but arbitrary Scheme objects.
> > > > But that requires changes at the OS level (or mapping them
> > > > to/from strings, which is a waste if both sides can handle
> > > > structured objects).
> > >
> > > !?  the ability to pass typed records around is an idea that was
> > > tarred, feathered, drawn and quartered by unix.  files, and therefore
> > > streams, have no type.  they are byte streams.
> >
> > I was not talking about "records" but s-expressions.  "json"
> > is kind of sort of the same thing. Without a generally useful
> > and simple such mechanism, people end up devising their own.
> > The 9p format for instance. And go has typed channels.
>
> it sounds like you're saying 9p isn't useful.  .... i must be reading
> your post incorrectly.

9p is quite useful. But the same semantics could've been
implemented using a more universal but compact structured
format such as s-expr. It is not the only choice but to me it
seems to strike a reasonable balance (compared to bloaty XML
at one extreme, tightly packed binary structures at another,
and byte streams with printf/parse encode/decode at the third
extreme).

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> On Tue, 28 Aug 2012 21:39:06 EDT erik quanstrom <quanstro@quanstro.net>  wrote:
> > > The feature I want is the ability to pass not just character
> > > values in environment or pipes but arbitrary Scheme objects.
> > > But that requires changes at the OS level (or mapping them
> > > to/from strings, which is a waste if both sides can handle
> > > structured objects).
> >
> > !?  the ability to pass typed records around is an idea that was
> > tarred, feathered, drawn and quartered by unix.  files, and therefore
> > streams, have no type.  they are byte streams.
>
> I was not talking about "records" but s-expressions.  "json"
> is kind of sort of the same thing. Without a generally useful
> and simple such mechanism, people end up devising their own.
> The 9p format for instance. And go has typed channels.

it sounds like you're saying 9p isn't useful.  .... i must be reading
your post incorrectly.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[Bakul Shah]

On Tue, 28 Aug 2012 21:39:06 EDT erik quanstrom <quanstro@quanstro.net>  wrote:
> > The feature I want is the ability to pass not just character
> > values in environment or pipes but arbitrary Scheme objects.
> > But that requires changes at the OS level (or mapping them
> > to/from strings, which is a waste if both sides can handle
> > structured objects).
>
> !?  the ability to pass typed records around is an idea that was
> tarred, feathered, drawn and quartered by unix.  files, and therefore
> streams, have no type.  they are byte streams.

I was not talking about "records" but s-expressions.  "json"
is kind of sort of the same thing. Without a generally useful
and simple such mechanism, people end up devising their own.
The 9p format for instance. And go has typed channels.

> rc already passes structured data through the environment.
> rc variables in the environment are defined as
>
> 	var:	[^ctl-a]*
> 		| ([^ctl-a]*) ctl-a list
>
> so there is precident for this in shells.

And this.

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> 	var:	[^ctl-a]*
> 		| ([^ctl-a]*) ctl-a list

sorry.  s/list/var/

- erik

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> The feature I want is the ability to pass not just character
> values in environment or pipes but arbitrary Scheme objects.
> But that requires changes at the OS level (or mapping them
> to/from strings, which is a waste if both sides can handle
> structured objects).

!?  the ability to pass typed records around is an idea that was
tarred, feathered, drawn and quartered by unix.  files, and therefore
streams, have no type.  they are byte streams.

one of the advantages of unix over, say, ibm systems, is that in unix
it is not the os' business to care what you're passing about.  but by
the same token, if you are the application, you get to arrange these
things by yourself.

rc already passes structured data through the environment.
rc variables in the environment are defined as

	var:	[^ctl-a]*
		| ([^ctl-a]*) ctl-a list

so there is precident for this in shells.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> On Tue, 28 Aug 2012 16:34:10 EDT erik quanstrom <quanstro@quanstro.net>  wrote:
> > my knee-jerk reaction to my own question is that making it easier
> > and more natural to parallelize dataflow.  a pipeline is just a really
> > low-level way to talk about it.  the standard
> > 	grep x *.[ch]
> > forces all the *.[ch] to be generated before 1 instance of grep runs on
> > whatever *.[ch] evaluates to be.
>
> Here the shell would have to understand program behavior.
> Consider something like
>
> 	8l x.8 y.8 z.8 ...
>
> This can't be parallelized (but a parallelizable loader can be
> written).

ya, ya.  improving on rc in a noticable way is hard.
and thinking aloud is a bad idea.  and a good way to look foolish.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[arisawa]

Hello,

On 2012/08/29, at 4:34, dexen deVries wrote:

> now i see i can do:
> 
> x=1 y=2 z=3
> 
> ...and only `z' retains its new value in the external scope, while `x' and `y' 
> are limited in scope.

No.

ar% a=1 b=2 c=3; echo $a $b $c
1 2 3
ar% a=() b=() c=()
ar% a=1 b=2 {c=3}; echo $a $b $c
3
ar% 

Kenji Arisawa

Re: [9fans] rc's shortcomings (new subject line)

[Bakul Shah]

On Tue, 28 Aug 2012 16:34:10 EDT erik quanstrom <quanstro@quanstro.net>  wrote:
> my knee-jerk reaction to my own question is that making it easier
> and more natural to parallelize dataflow.  a pipeline is just a really
> low-level way to talk about it.  the standard
> 	grep x *.[ch]
> forces all the *.[ch] to be generated before 1 instance of grep runs on
> whatever *.[ch] evaluates to be.

Here the shell would have to understand program behavior.
Consider something like

	8l x.8 y.8 z.8 ...

This can't be parallelized (but a parallelizable loader can be
written).

May be you can define a `par' command (sort of like xargs but
invokes in parallel).

	echo *.[ch] | par -1 grep x

> but it would be okay for almost every use of this if *.[ch] were generated
> in parallel with any number of grep's being run.
>
> i suppose i'm stepping close to sawzall now.

Be careful!

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> > the haahr/rakitzis es' if makes more sense, even if it's wierder.)
> 
> Agreed; es would be an interesting starting point for a new shell.

es is great input.  there are really cool ideas there, but it does
seem like a lesson learned to me, rather than a starting point.

> I think in order to really answer that question, one would have to
> step back for a moment and really think about what one wants out of a
> shell.  There seems to be a natural conflict a programming language
> and a command interpreter (e.g., the 'if' vs. 'if not' thing).  On
> which side does one err?

since the raison d'être of a shell is to be a command interpter, i'd
go with that.

> I tend to agree.  As a command interpreter, rc is more or less fine as
> is.  I'd really only feel motivated to change whatever people felt
> were common nits, and there are fairly few of those.

there are nits of omission, and those can be fixable.  ($x(n-m) was added)

> > perhaps (let's hope) someone else has better ideas.
> 
> Well, something off the top of my head: Unix pipelines are sort of
> like chains of coroutines.  And they work great for defining linear
> combinations of filters.  But something that may be interesting would
> be the ability to allow the stream of computations to branch; instead
> of pipelines being just a list, make them a tree, or even some kind of
> dag (if one allows for the possibility of recombining streams).  That
> would be kind of an interesting thing to play with in a shell
> language; I don't know how practically useful it would be, though.

rc already has non-linear pipelines.  but they're not very convienient.

i think part of the problem is answering the question, what problem
would we like to solve.  because "a better shell" just isn't well-defined
enough.

my knee-jerk reaction to my own question is that making it easier
and more natural to parallelize dataflow.  a pipeline is just a really
low-level way to talk about it.  the standard
	grep x *.[ch]
forces all the *.[ch] to be generated before 1 instance of grep runs on
whatever *.[ch] evaluates to be.

but it would be okay for almost every use of this if *.[ch] were generated
in parallel with any number of grep's being run.

i suppose i'm stepping close to sawzall now.

- erik

Re: [9fans] rc's shortcomings (new subject line)

[Aram Hăvărneanu]

> But something that may be interesting would
> be the ability to allow the stream of computations to branch; instead
> of pipelines being just a list, make them a tree, or even some kind of
> dag (if one allows for the possibility of recombining streams).

Rc has this. It's great. See section 10 of the rc paper or <{command}
in the rc manual. I use it all the time to see differences between
programmatically generated things.

-- 
Aram Hăvărneanu

Re: [9fans] rc's shortcomings (new subject line)

[Bakul Shah]

On Wed, 29 Aug 2012 01:11:26 +0530 Dan Cross <crossd@gmail.com>  wrote:
> On Tue, Aug 28, 2012 at 8:56 PM, erik quanstrom <quanstro@quanstro.net> wro=
>
> > perhaps (let's hope) someone else has better ideas.
>
> Well, something off the top of my head: Unix pipelines are sort of
> like chains of coroutines.  And they work great for defining linear
> combinations of filters.  But something that may be interesting would
> be the ability to allow the stream of computations to branch; instead
> of pipelines being just a list, make them a tree, or even some kind of
> dag (if one allows for the possibility of recombining streams).  That
> would be kind of an interesting thing to play with in a shell
> language; I don't know how practically useful it would be, though.

Coming up with an easy to use syntax for computation trees (or
arbitrary nets) is the hard part. May be the time is ripe for
a net-rc or net-scheme-shell.

The feature I want is the ability to pass not just character
values in environment or pipes but arbitrary Scheme objects.
But that requires changes at the OS level (or mapping them
to/from strings, which is a waste if both sides can handle
structured objects).

Re: [9fans] rc's shortcomings (new subject line)

[Bakul Shah]

On Tue, 28 Aug 2012 14:44:40 EDT erik quanstrom <quanstro@quanstro.net>  wrote:
> >=20
> > switch/case would make helluva difference over nested if/if not, if
> > defaulted to fall-through.
>
> maybe you have an example?  because i don't see that.  if not works
> fine, and can be nested.  case without fallthrough is also generally
> what i want.  if not, i can make the common stuff a function.
>
> > variable scoping (better than subshel) would help writing larger
> > scripts, but that's not necessarily an improvement ;-) something
> > similar to LISP's `let' special form, for dynamic binding.
>
> there is variable scoping.  you can write
>
> 	x=3D() y=3D() cmd
>
> cmd can be a function body or whatever.  x and y are then private
> to cmd.  you can nest redefinitions. =20
>
> 	x=3D1 y=3D2 {echo first $x $y; x=3Da y=3Db {echo second $x $y; x=3D=CE=
> B1=
>  y=3D=CE=B2 {echo third $x $y}; echo ret second $x $y}; echo ret first $x=
>  $y}
> 	first 1 2
> 	second a b
> 	third =CE=B1 =CE=B2
> 	ret second a b
> 	ret first 1 2

This is basically the same as let. Instead of
    let x=1 y=2 foo
you say
    x=1 y=2 foo
and this is lexical scoping. try

    lex=1 { echo $lex; }
    echo $lex
vs
    { var=1; echo $var; }
    echo $var

Re: [9fans] rc's shortcomings (new subject line)

[Dan Cross]

On Tue, Aug 28, 2012 at 8:56 PM, erik quanstrom <quanstro@quanstro.net> wrote:
>> And rc is not perfect.  I've always felt like the 'if not' stuff was a kludge.
>
> no, it's certainly not.  (i wouldn't call if not a kludge—just ugly.

Kludge perhaps in the sense that it seems to be to work around an
issue with the grammar and the expectation that it's mostly going to
be used interactively, as opposed to programmatically.  See below.

> the haahr/rakitzis es' if makes more sense, even if it's wierder.)

Agreed; es would be an interesting starting point for a new shell.

> but the real question with rc is, what would you fix?

I think in order to really answer that question, one would have to
step back for a moment and really think about what one wants out of a
shell.  There seems to be a natural conflict a programming language
and a command interpreter (e.g., the 'if' vs. 'if not' thing).  On
which side does one err?

> i can only think of a few things around the edges.  `{} and $ are
> obvious and is some way to use standard regular expressions.  but
> those really aren't that motivating.  rc does enough.

I tend to agree.  As a command interpreter, rc is more or less fine as
is.  I'd really only feel motivated to change whatever people felt
were common nits, and there are fairly few of those.

> perhaps (let's hope) someone else has better ideas.

Well, something off the top of my head: Unix pipelines are sort of
like chains of coroutines.  And they work great for defining linear
combinations of filters.  But something that may be interesting would
be the ability to allow the stream of computations to branch; instead
of pipelines being just a list, make them a tree, or even some kind of
dag (if one allows for the possibility of recombining streams).  That
would be kind of an interesting thing to play with in a shell
language; I don't know how practically useful it would be, though.

>> switch/case would make helluva difference over nested if/if not, if
>> defaulted to fall-through.
>
> maybe you have an example?  because i don't see that.  if not works
> fine, and can be nested.  case without fallthrough is also generally
> what i want.  if not, i can make the common stuff a function.
>
>> variable scoping (better than subshel) would help writing larger
>> scripts, but that's not necessarily an improvement ;-) something
>> similar to LISP's `let' special form, for dynamic binding.

(A nit: 'let' actually introduces lexical scoping in most Lisp
variants; yes, doing (let ((a 1)) ...) has non-lexical effect if 'a'
is a dynamic variable in Common Lisp, but (let) doesn't itself
introduce dynamic variables.  Emacs Lisp is a notable exception in
this regard.)

> there is variable scoping.  you can write
>
>         x=() y=() cmd
>
> cmd can be a function body or whatever.  x and y are then private
> to cmd.  you can nest redefinitions.
>
>         x=1 y=2 {echo first $x $y; x=a y=b {echo second $x $y; x=α y=β {echo third $x $y}; echo ret second $x $y}; echo ret first $x $y}
>         first 1 2
>         second a b
>         third α β
>         ret second a b
>         ret first 1 2

This syntax feels clunky and unfamiliar to me; rc resembles block
scoped languages like C; I'd rather have a 'local' or similar keyword
to introduce a variable in the scope of each '{ }' block.

> you should try the es shell.  es had let and some other scheme-y
> features.  let allows one to do all kinds of tricky stuff, like build
> a shell debugger in the shell, but my opinion is that es was more
> powerful and fun, but it didn't buy enough because it didn't really
> expand on the essential nature of a shell.  what can one do to
> manipulate processes and file descriptors.

es was a weird merger between rc's syntax and functional programming
concepts.  It's neat-ish, but unless we're really ready to go to the
pipe monad (not that weird, in my opinion) you're right.  Still, if it
allowed one to lexically bind a file descriptor to a variable, I could
see that being neat; could I have a closure over a file descriptor?  I
don't think the underlying process model is really set up for it, but
it would be kind of cool: one could have different commands consuming
part of a stream in a very flexible way.

        - Dan C.

Re: [9fans] rc's shortcomings (new subject line)

[dexen deVries]

On Tuesday 28 of August 2012 14:44:40 erik quanstrom wrote:
> (...)
> > variable scoping (better than subshel) would help writing larger
> > scripts, but that's not necessarily an improvement ;-) something
> > similar to LISP's `let' special form, for dynamic binding.
>
> there is variable scoping.  you can write
>
> 	x=() y=() cmd

thank you good sire, for you've just made my day.


now i see i can do:

x=1 y=2 z=3

...and only `z' retains its new value in the external scope, while `x' and `y'
are limited in scope.


horray for rc and helpful 9fans,
--
dexen deVries

1972 - Dennis Ritchie invents a powerful gun that shoots both forward and
backward simultaneously. Not satisfied with the number of deaths and permanent
maimings from that invention he invents C and Unix.

Re: [9fans] rc's shortcomings (new subject line)

[erik quanstrom]

> 
> switch/case would make helluva difference over nested if/if not, if
> defaulted to fall-through.

maybe you have an example?  because i don't see that.  if not works
fine, and can be nested.  case without fallthrough is also generally
what i want.  if not, i can make the common stuff a function.

> variable scoping (better than subshel) would help writing larger
> scripts, but that's not necessarily an improvement ;-) something
> similar to LISP's `let' special form, for dynamic binding.

there is variable scoping.  you can write

	x=() y=() cmd

cmd can be a function body or whatever.  x and y are then private
to cmd.  you can nest redefinitions.  

	x=1 y=2 {echo first $x $y; x=a y=b {echo second $x $y; x=α y=β {echo third $x $y}; echo ret second $x $y}; echo ret first $x $y}
	first 1 2
	second a b
	third α β
	ret second a b
	ret first 1 2

you should try the es shell.  es had let and some other scheme-y
features.  let allows one to do all kinds of tricky stuff, like build
a shell debugger in the shell, but my opinion is that es was more
powerful and fun, but it didn't buy enough because it didn't really
expand on the essential nature of a shell.  what can one do to
manipulate processes and file descriptors.

- erik