I didn't mean to imply that I wanted to replace the number with tags,
what I meant to imply is that the number of lines is not any better
than START and BEGIN tags, while a fixed width count of bytes (even a
number string padded to a constant number of bytes with zeroes) is
better.
On Mon, Mar 21, 2011 at 6:14 AM, Chas Emerick <cemer...@snowtide.com> wrote:
>
> On Mar 21, 2011, at 8:52 AM, James Reeves wrote:
>
>> On 21 March 2011 11:29, Chas Emerick <cemer...@snowtide.com> wrote:
>>> The notion of "passing around Clojure data structures" does get watered
>>> down because of the non-sexpr-nature of e.g. *out* and *err*, and it's all
>>> message-oriented so as to support asynchronous evaluation from the same
>>> client, but that's pretty much what nREPL does. Expressions are sent,
>>> results are printed and sent back.
>>
>> That wasn't quite what I meant :)
>>
>> You could use a Clojure data structure protocol (henceforth known as
>> CDSP) to send the just data you want evaluated by the REPL, e.g.
>>
>>>>> (+ 1 1)
>> <<< 2
>>
>> But that's probably too simplistic. Instead, you'd probably encase
>> messages in a map, e.g.
>>
>>>>> {:id 1, :eval (+ 1 1)}
>> <<< {:id 1, :return 2}
>>
>> Which would allow you to handle more sophisticated streaming stuff as well:
>>
>>>>> {:id 2, :eval (do (Thread/sleep 1) (print "world"))}
>>>>> {:id 3, :eval (print "hello")}
>> <<< {:id 3, :out "hello"}
>> <<< {:id 3, :return nil}
>> <<< {:id 2, :out "world"}
>> <<< {:id 2, :return nil}
>>
>> My point was more that network protocols should be designed in layers.
>> Take a streaming protocol like TCP, layer netstrings on top of it so
>> you have a safe way of passing fixed-length messages. Then use the
>> Clojure read-string and pr-str functions to encode data.
>>
>> You then have a very basic protocol that allows you to communicate in
>> more complex data structures, like maps, vectors and lists, which you
>> can use as a basis for a more sophisticated protocol.
>>
>> In essence, we want to build a compound network protocol out of simple
>> components. You don't have to use netstrings and Clojure data
>> structures to do it, but they seem like a good fit.
>
> I think we're in violent agreement. Here's a sample nREPL exchange from
> https://github.com/clojure/tools.nrepl:
>
>> [catapult:~] chas% telnet localhost <port-number>
>> Trying 127.0.0.1...
>> Connected to localhost.
>> Escape character is '^]'.
>> 2
>> "id"
>> "foo"
>> "code"
>> "(println 5)"
>> 3
>> "ns"
>> "user"
>> "id"
>> "foo"
>> "value"
>> "nil\n"
>> 3
>> "ns"
>> "user"
>> "out"
>> "5\n"
>> "id"
>> "foo"
>> 3
>> "status"
>> "done"
>> "ns"
>> "user"
>> "id"
>> "foo"
>
>
> It's probably not clear from the listing, but only the first message is being
> sent; the next three are received. There's really not a lot of
> sophistication here; indeed, it's even less sophisticated than if the
> messages were being sent using sexpressions, that that would require a lisp
> reader and printer (of some diminished capacity, presumably) on the client
> side.
>
> As Kevin was saying elsewhere, the entry count that precedes each message
> could be replaced with a terminator, or start and end tags if one so wishes.
> Those that really, really like sexpressions might use braces:
>
> {"id"
> "foo"
> "code"
> "(println 5)"}
>
> I considered doing this, but thought it better to not imply that the protocol
> allowed for any ol' readable data structure to be passed along.
>
> - Chas
>
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And what is good, Phaedrus,
And what is not good—
Need we ask anyone to tell us these things?
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