[racket] users Digest, Vol 109, Issue 57

Please take me off the list

Thanks

On Thu, Sep 25, 2014 at 1:04 PM,  <users-request at racket-lang.org> wrote:
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> Today's Topics:
>
>    1. htdp: exercise 21.1.3 (Daniel Bastos)
>    2. Re: web server: module servlets (George Neuner)
>    3. ANN: DOS, Delimited-continuation-based Operating-system
>       Simulator (Jay McCarthy)
>    4. Re: web server: module servlets (Jay McCarthy)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 25 Sep 2014 13:48:05 -0300
> From: Daniel Bastos <dbastos at toledo.com>
> To: Racket Users <users at racket-lang.org>
> Subject: [racket] htdp: exercise 21.1.3
> Message-ID:
>         <CAB08-qr1MMDnJ6uSztfx+qnJMGh3QYztK5iC3_xWiMhKz-onFA at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> The solution is missing, but I thought of exposing this one here so that it
> gets scrutinized before sending it to Robby Findler.
>
> ;; Exercise 21.1.3. Define natural-f, which is the abstraction of the
> ;; following two functions:
> ;;
> ;; ;; copy : N X  ->  (listof X)
> ;; ;; to create a list that contains
> ;; ;; obj n times
> ;; (define (copy n obj)
> ;;   (cond
> ;;     [(zero? n) empty]
> ;;     [else (cons obj
> ;;                 (copy (sub1 n) obj))]))
> ;;
> ;; ;; n-adder : N number  ->  number
> ;; ;; to add n to x using
> ;; ;; (+ 1 ...) only
> ;; (define (n-adder n x)
> ;;   (cond
> ;;     [(zero? n) x]
> ;;     [else (+ 1
> ;;              (n-adder (sub1 n) x))]))
> ;;
> ;; Don't forget to test natural-f. Also use natural-f to define
> ;; n-multiplier, which consumes n and x and produces n times x with
> ;; additions only. Use the examples to formulate a contract.
> ;;
> ;; Hint: The two function differ more than, say, the functions sum and
> ;; product in exercise 21.1.2. In particular, the base case in one
> ;; instance is a argument of the function, where in the other it is just
> ;; a constant value.
> ;;
> ;; (*) Solution
> ;;
> ;; After following the design recipe for abstraction, we get natural-f as
> ;; shown below. To write the contract, let's first only consider copy,
> ;; then we consider only n-adder and then we consider both.
> ;;
> ;; ;; natural-f-copy: Nat X (X (listof X) -> (listof X)) (listof X) ->
> (listof X)
> ;; ;; natural-f-adder: Nat number (number number -> number) number -> number
> ;;
> ;; The contract for natural-f-adder is more specific than
> ;; natural-f-copy. The difference between these is that in the first, two
> ;; different types are involved --- X and (listof X). Therefore, (listof
> ;; X) works as another variable, so let's call it Y in the final version.
>
> ;; natural-f: Nat X (X Y -> Y) Y -> Y
> (define (natural-f n x f init)
>   (cond
>     [(zero? n) init]
>     [else (f x
>               (natural-f (sub1 n) x f init))]))
>
> ;; (*) Tests
>
> ;; Let's use two different types in copy, say symbol and then number.
>
> (check-expect (copy 3 'a) '(a a a))
> (check-expect (natural-f 3 'a cons empty) (copy 3 'a))
>
> (check-expect (copy 0 'a) empty)
> (check-expect (natural-f 0 'a cons empty) (copy 0 'a))
>
> (check-expect (copy 3 1) (list 1 1 1))
> (check-expect (natural-f 3 1 cons empty) (copy 3 1))
>
> ;; For n-adder, let's make sure to test different init-values.
>
> (check-expect (n-adder 3 3.14) 6.14)
> (check-expect (natural-f 3 1 + 3.14) (n-adder 3 3.14))
>
> (check-expect (n-adder 3 1) 4)
> (check-expect (natural-f 3 1 + 1) (n-adder 3 1))
>
> (check-expect (n-adder 3 2) 5)
> (check-expect (natural-f 3 1 + 2) (n-adder 3 2))
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> ------------------------------
>
> Message: 2
> Date: Thu, 25 Sep 2014 12:51:56 -0400
> From: George Neuner <gneuner2 at comcast.net>
> To: Jay McCarthy <jay.mccarthy at gmail.com>
> Cc: users <users at racket-lang.org>
> Subject: Re: [racket] web server: module servlets
> Message-ID: <5424482C.1030901 at comcast.net>
> Content-Type: text/plain; charset="utf-8"; Format="flowed"
>
> Hi Jay,
>
> On 9/23/2014 10:03 PM, Jay McCarthy wrote:
>> The command-line tool is basically deprecated and only provided for
>> backwards compatibility. There is a huge amount that it can't do at
>> all and it hasn't been the primary way that we recommend using the Web
>> server for a very long time.
>
> I'm not using the plt-web-server app - I created a minimal application
> that set up the environment: directories, ports, etc. and a start
> function that just returns a 404 if called.  My server sits behind
> Apache and only handles servlets, which I would like to be demand load
> modules so they can be added to and updated easily. That's why I am
> interested in being able to unload servlets on command, though not
> necessarily all of them at once (although that also is helpful).
>
>
>> > Not really knowing much about Racket's internals he naively asks:
>> >Coulda server  pre-load the commonly used webserver modules and make
>> >themavailableto new module servlets, or does the custodian
>> >implementation  make doing thatdifficult/impossible?
>>
>> This is the purpose of the make-servlet-namespace argument of
>> configuration-table->web-config@ but there is no option in the
>> configuration file for that argument.
>>
>> http://docs.racket-lang.org/web-server-internal/Web_Servers.html?q=servlet-namespace#%28def._web-config._%28%28lib._web-server%2Fweb-config-unit..rkt%29._configuration-table-~3eweb-config~40%29%29
>
> The namespace facility seems designed more for user written modules than
> for library modules.
>
> My analysis may be off-base as I have very little experience working
> directly with custodians, but it seems that when a dynamic servlet is
> first loaded, its custodian spends a lot of additional time (re)loading
> library modules that already exist in other custodians. [ Though I can't
> tell exactly what's happening, I can see a lot of disk activity when I
> think I'm loading a 5KB servlet. ]  Reasonably I would have expected
> that after loading/linking the first servlet, the libraries common to
> the servlets would be already in memory. But loading additional servlets
> is no quicker [ and causes a similar disk hit ] so clearly I don't
> understand what is happening internally with the custodians.
>
> If a Racket library is deliberately put into the servlet-namespace, does
> that streamline linking?
>
>
>> > My application so far is based on stateful servlets and AJAX ... stateful
>> > mainly because it's easier for me to understand.  Currently there is
>> >little use ofcontinuations, but some planned functionality will use them
>> >  extensively and it certainly wouldhelp if debugging didn't always mean
>> >starting over setting up conditions in theapplication.
>>
>> This comment/question is related to questions 4 and 5 from the FAQ:
>>
>> http://docs.racket-lang.org/web-server/faq.html?q=servlet-namespace#%28part._update-servlets%29
>
> That link leads to a "troubleshooting" page 8-).  I didn't consider the
> issue to be a "problem" per se - I already knew that restarting a
> stateful servlet would lose saved state.  Most of my existing servlets
> are one-shots that don't save any state, but they are written using the
> stateful language.  Only a few use continuations and not extensively (so
> far).  I was just thinking ahead to stuff that will need to use
> continuations more extensively.
>
> Thanks for putting up with my questions.
> George
>
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> ------------------------------
>
> Message: 3
> Date: Thu, 25 Sep 2014 13:02:00 -0400
> From: Jay McCarthy <jay.mccarthy at gmail.com>
> To: users <users at racket-lang.org>
> Subject: [racket] ANN: DOS,     Delimited-continuation-based
>         Operating-system Simulator
> Message-ID:
>         <CAJYbDam0maAG7ZmCBjbha1uqhJyCpX9J+L3=kxqAL4GjdKUvkg at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
> I've just released the game architecture library I talked about in
> part 2 of my RacketCon talk.
>
> The big picture of this library is to make World-style programs more
>  compositional by (a) using continuations to hide the internal state
> (including control state) of components and (b) using environments as
> a standard monoid-based inter-component communication channel. A
> monoid is used to ensure that the components can be evaluated in any
> order. Despite assumptions some have about continuations and pure
> functional programming, it is incredibly efficient and can run at
> 60FPS, as demonstrated in get-bonus.
>
> You can get it with
>
> raco pkg install dos
>
> And you can try out the demo with
>
> racket -l dos/examples/win
>
> The demo source is a bare 39 lines:
>
> https://github.com/jeapostrophe/dos/blob/master/dos/examples/win.rkt
>
> and I provide the non-DOS version for comparison:
>
> https://github.com/jeapostrophe/dos/blob/master/dos/examples/win-long.rkt
>
> The core library has a mere 36 lines:
>
> https://github.com/jeapostrophe/dos/blob/master/dos/main.rkt
>
> --
> Jay McCarthy
> http://jeapostrophe.github.io
>
>            "Wherefore, be not weary in well-doing,
>       for ye are laying the foundation of a great work.
> And out of small things proceedeth that which is great."
>                           - D&C 64:33
>
>
> ------------------------------
>
> Message: 4
> Date: Thu, 25 Sep 2014 13:04:44 -0400
> From: Jay McCarthy <jay.mccarthy at gmail.com>
> To: George Neuner <gneuner2 at comcast.net>
> Cc: users <users at racket-lang.org>
> Subject: Re: [racket] web server: module servlets
> Message-ID:
>         <CAJYbDa=-DuRMVy7JnCt32Y8waG2+qkHZQw5cVDL4L_d6zth45w at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
> On Thu, Sep 25, 2014 at 12:51 PM, George Neuner <gneuner2 at comcast.net> wrote:
>> Hi Jay,
>>
>> On 9/23/2014 10:03 PM, Jay McCarthy wrote:
>>
>> The command-line tool is basically deprecated and only provided for
>> backwards compatibility. There is a huge amount that it can't do at
>> all and it hasn't been the primary way that we recommend using the Web
>> server for a very long time.
>>
>>
>> I'm not using the plt-web-server app - I created a minimal application that
>> set up the environment: directories, ports, etc. and a start function that
>> just returns a 404 if called.  My server sits behind Apache and only handles
>> servlets, which I would like to be demand load modules so they can be added
>> to and updated easily.  That's why I am interested in being able to unload
>> servlets on command, though not necessarily all of them at once (although
>> that also is helpful).
>>
>>
>>> Not really knowing much about Racket's internals he naively asks:
>>> Could a server  pre-load the commonly used webserver modules and make
>>> them available to new module servlets, or does the custodian
>>> implementation make doing that difficult/impossible?
>>
>> This is the purpose of the make-servlet-namespace argument of
>> configuration-table->web-config@ but there is no option in the
>> configuration file for that argument.
>>
>> http://docs.racket-lang.org/web-server-internal/Web_Servers.html?q=servlet-namespace#%28def._web-config._%28%28lib._web-server%2Fweb-config-unit..rkt%29._configuration-table-~3eweb-config~40%29%29
>>
>>
>> The namespace facility seems designed more for user written modules than for
>> library modules.
>>
>> My analysis may be off-base as I have very little experience working
>> directly with custodians, but it seems that when a dynamic servlet is first
>> loaded, its custodian spends a lot of additional time (re)loading library
>> modules that already exist in other custodians.  [ Though I can't tell
>> exactly what's happening, I can see a lot of disk activity when I think I'm
>> loading a 5KB servlet. ]  Reasonably I would have expected that after
>> loading/linking the first servlet, the libraries common to the servlets
>> would be already in memory.  But loading additional servlets is no quicker [
>> and causes a similar disk hit ] so clearly I don't understand what is
>> happening internally with the custodians.
>>
>> If a Racket library is deliberately put into the servlet-namespace, does
>> that streamline linking?
>>
>
> Your assumption about the purpose of this is not correct. Anything in
> the servlet-namespace will be shared between all servlets, and thus
> not loaded per-servlet.
>
>>> My application so far is based on stateful servlets and AJAX ... stateful
>>> mainly because it's easier for me to understand.  Currently there is
>>> little use of continuations, but some planned functionality will use them
>>> extensively and it certainly would help if debugging didn't always mean
>>> starting over setting up conditions in the application.
>>
>> This comment/question is related to questions 4 and 5 from the FAQ:
>>
>> http://docs.racket-lang.org/web-server/faq.html?q=servlet-namespace#%28part._update-servlets%29
>>
>>
>> That link leads to a "troubleshooting" page 8-).  I didn't consider the
>> issue to be a "problem" per se - I already knew that restarting a stateful
>> servlet would lose saved state.  Most of my existing servlets are one-shots
>> that don't save any state, but they are written using the stateful language.
>> Only a few use continuations and not extensively (so far).  I was just
>> thinking ahead to stuff that will need to use continuations more
>> extensively.
>>
>> Thanks for putting up with my questions.
>> George
>>
>
>
>
> --
> Jay McCarthy
> http://jeapostrophe.github.io
>
>            "Wherefore, be not weary in well-doing,
>       for ye are laying the foundation of a great work.
> And out of small things proceedeth that which is great."
>                           - D&C 64:33
>
>
> End of users Digest, Vol 109, Issue 57
> **************************************