[racket] REPL input chunking for non-sexp language

Why do you need a weird two-phase reading system to deal with the EOF issue?

Robby

On Monday, December 10, 2012, Jay McCarthy wrote:

> The datalog language tries to do this too.
>
> There's a repl-submit? predicate you can use and I have weird two-phase
> reading system to deal with the EOF issue:
>
>
> https://github.com/plt/racket/blob/master/collects/datalog/lang/configure-runtime.rkt
>
> https://github.com/plt/racket/blob/master/collects/datalog/tool/submit.rkt
>
> Jay
>
>
> On Mon, Dec 10, 2012 at 8:04 AM, Matthew Flatt <mflatt at cs.utah.edu<javascript:_e({}, 'cvml', 'mflatt at cs.utah.edu');>
> > wrote:
>
>> When you run plain `racket', the REPL is `read-eval-print-loop', which
>> uses `(current-prompt-read)', `(current-eval)', and `(current-print)'.
>>
>> Any line-editing capability is whatever the terminal does, which
>> normally means that input is sent to the reader when you hit Return.
>> Even if you load `readline' or `xrepl', a Return commits a line of
>> characters to be sent off to the reader.
>>
>> The delivery of an expression to the evaluator, however, is determined
>> by the reader. That is, if your reader sees a "fun" that should match
>> an "end", then it should keep reading input characters until it sees
>> the "end". When the reader returns a datum, then it's passed off to the
>> evaluator.
>>
>> (If an interactive EOF is needed to terminate a form for your reader,
>> that shouldn't necessarily make the REPL quit. The REPL should quit
>> only when the reader returns an EOF. So, a reader might consume an
>> interactive EOF as a terminator, and then it can continue reading the
>> next time around.)
>>
>> If I remember correctly, DrRacket is a little different. A Return in
>> DrRacket takes the text so far and implicitly adds an EOF to the end.
>> If the reader applied to that text raises `exn:fail:read:eof', then
>> DrRacket it as an indication that the expression isn't finished, and so
>> it lets the user keep editing on the next line. Meanwhile, an
>> `exn:fail:read' exception other than the subtype `exn:fail:read:eof'
>> means that the read error should be reported to the user.
>>
>>
>> At Sun, 9 Dec 2012 19:03:44 -0500, Daniel Patterson wrote:
>> > I'm working (with sk and jpolitz) on a non-sexp language built on top
>> > of racket.
>> >
>> > We have basic support for it in the repl inside DrRacket, but none at
>> > all from the racket commandline repl (which also means no support for
>> > embedding inside other editors) - and the former seems to be using
>> > s-exps to figure out when to send the input to our eval (I think - I
>> > haven't found documentation describing how this works).
>> >
>> > So my question is:
>> >
>> > Is there a way to specify how input is split before sending to eval,
>> > both so that DrRacket could follow our conventions (which might, for
>> > example, match a "fun" with matching "end"), and so that the
>> > commandline repl knows how to split input at all (as right now it just
>> > keeps waiting for input until EOF - and EOF also causes the repl to
>> > quit!) Is there something that read/read-syntax should signal, or
>> another
>> > handler to use?
>> >
>> > Thanks!
>> > Daniel
>> > ____________________
>> >   Racket Users list:
>> >   http://lists.racket-lang.org/users
>> ____________________
>>   Racket Users list:
>>   http://lists.racket-lang.org/users
>>
>
>
>
> --
> Jay McCarthy <jay at cs.byu.edu <javascript:_e({}, 'cvml',
> 'jay at cs.byu.edu');>>
> Assistant Professor / Brigham Young University
> http://faculty.cs.byu.edu/~jay
>
> "The glory of God is Intelligence" - D&C 93
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20121210/f175dcdf/attachment.html>