Arc Forumnew | comments | leaders | submitlogin
37 points by elibarzilay 2272 days ago | link | parent

With the PLT web server:

  (define cc (make-parameter #f))

  (define (input name) `(input ((type "text") (name ,(format "~a" name)))))
  (define (submit) `(input ((type "submit"))))
  (define (form . body) `(form ((action ,(cc))) ,@body))
  (define (a ref . body) `(a ((href ,ref)) ,@body))
  (define-syntax page
    (syntax-rules ()
      [(page x ...) (send/suspend (lambda (k) (cc k) `(html (body ,x ...))))]))
  (define (get name req)
    (extract-binding/single name (request-bindings req)))

  (define (start initial-request)
    (define foo (get 'foo (page (form (input 'foo) (submit)))))
    (page (a (cc) "click here"))
    (page "you said: " foo))


38 points by GreyLensman 2272 days ago | link

What is worth noting in the above post is the "With the PLT web server" part.

What I mean is most of the other posts demo how to do it with some required (exotic) framework. This example is just using the basic web server APIs of the PLT continuation based web server.

In other words in this example, Eli BOTH writes the framework (in the first 9 lines), then uses the framework in the last 4 lines.

PLT's mzscheme is in effect, a very distant cousin to Scheme. If they weren't all eggheads and had at least one attentive marketing person, they would have labeled it some new fangled SuperLispIncarnateNextGeneration (SLING) moniker and received a bit of buzz.

I haven't looked at exactly how PG implemented Arc over MzScheme, but consider this. Much of what he did _could_ be done using no more then PLT mzscheme's out of the box, macro system, custom language module capability and custom reader capability, by anyone. Yes, even you.

In some sense most of Arc is just what anyone does who develops in PLTs Scheme/laguage system, i.e., create their own custom language/DSL. PG's may have done it a bit better, more extensively, with a general purpose intent.

So what is the secret weapon here Arc, or the underlying system that allows someone to create an Arc so easily?

You could, right now, be using PLT MzScheme to do your own Arc(s), your own, just for you and your friends custom language/DSL.

Ruby, Python are cute, and deserve having a user base, but PLT mzscheme is without doubt, the best and most powerful language system out there that "no one talks about."

-----

19 points by matthiasf 2271 days ago | link

Thanks for the highly accurate description of PLT and PLT Scheme. I founded PLT as an academic but I am one who appreciates the necessity to open a channel of communication between the 'real' world and academia.

While Matthew and Robby are the "drivers" (with lots of co-pilots :-) I think that setting this tone early in the project has placed PLT Scheme naturally in a lonely niche: it is a real scripting language with capabilities that rival those of everything out there and it is also a serious academic infrastructure. Typed Scheme -- the first and only sound 'gradual typing' language so far -- is just an example of what I mean. We can publish about this in the flagship research conference on programming languages and at the same time, we are using it for its intended applications. Sam Tobin-Hochstadt is porting a part of DrScheme to Typed Scheme as I type. It is this kind of experiment -- porting a piece that your "life" depends on -- that puts us squarely on the applied side, too.

-- Matthias

-----

2 points by NickSmith 2270 days ago | link

Thanks Grey. I am in the process of teaching myself Scheme (via SIPS) and find your comment quite enlightening.

-----

2 points by croach 2269 days ago | link

Hi Nick,

I'm currently in the process of teaching myself Scheme as well through a combination of HtDP and SICP and I was wondering what SIPS is? Perhaps it's another source I should check into.

-----

1 point by NickSmith 2269 days ago | link

I perhaps need to first teach myself to type. I meant SICP.

-----

1 point by croach 2268 days ago | link

Heh, that's funny and disappointing all at the same time--I was really hoping there was another really great resource on the web for learning Scheme. Thanks for the reply.

-----

4 points by NickSmith 2267 days ago | link

Sorry to disappoint, but here's a book that I do recommend: http://www.amazon.com/Little-Schemer-Daniel-P-Friedman/dp/02...

It's quite short and set out in a question and answers style. The thing is, it very gently and very subtlety bends your mind around to the Lisp way of thinking. After reading this, SICP seems so much more accessible.

There are also two follow on books - The Reasoned Schemer and The Seasoned Schemer which are again quite short and use the same interactive approach. I haven't had chance to read them yet but they get rave reviews on Amazon

-----

2 points by vincenz 2269 days ago | link

Out of curiousity,

How do you run this?

-----

6 points by willpost 2269 days ago | link

Not really Arc related, but here you go in 3 steps:

1 - Paste the following code into a new document test.ss and save in servlet example folder (/usr/plt/collects/web-server/default-web-root/servlets/examples/test.ss) If document name test.ss changes, change the module name on first line.

(module test mzscheme (require (lib "servlet.ss" "web-server")) (provide (all-defined)) (define interface-version 'v1) (define timeout +inf.0)

  (define cc (make-parameter #f))

  (define (input name) `(input ((type "text") (name ,(format "~a" name)))))
  (define (submit) `(input ((type "submit"))))
  (define (form . body) `(form ((action ,(cc))) ,@body))
  (define (a ref . body) `(a ((href ,ref)) ,@body))
  (define-syntax page
    (syntax-rules ()
      [(page x ...) (send/suspend (lambda (k) (cc k) `(html (body ,x ...))))]))
  (define (get name req)
    (extract-binding/single name (request-bindings req)))

  (define (start initial-request)
    (define foo (get 'foo (page (form (input 'foo) (submit)))))
    (page (a (cc) "click here"))
    (page "you said: " foo))
  
)

2 - Start the PLT web server sudo /usr/plt/bin/plt-web-server

3 - Open a web browser and navigate to http://localhost/servlets/examples/test.ss

An easy way to check for errors is to open it in DrScheme, click "Run" and they would be highlighted in red.

-----