I've been working on a Web site written in PLT Scheme, and I'm no longer able to do so. What I've written so far uses a lot of x-expressions and calls to Ryan's PostgreSQL library. If anyone on the list wants to take over for me, let me know. -- Paul _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-scheme
Well, here's the scenario I had in mind when I originally posed the question
about class variables. I've since come up with a way to accomplish this
without using classes at all, so this may be a moot point, but here it is.
My idea was an x-expression based template library, where each template was
enclosed in a class. The concept was based on some existing text templating
languages, where a template can contain "blocks" that a derived template can
override, and "parameters" that can be set on a per-instance basis. In this
case the template expression would be associated with the class itself,
while the parameter values would be associated with an instance.
I wanted a syntax where default block and parameter values could be
specified in-line in the template rather than as default parameters to a
function. And I wanted to be able to nest blocks.
I should mention that if this were to be implemented using protected static
fields, they would be treated as read-only. I have not been able to come up
with a realistic use case for *mutable* protected static fields, which in
fact sound a little scary.
A simple example of one of these templates would look something like:
'(html
(head
(block: head
(title (param: title "Page title"))
(link ((rel "StyleSheet")
("/static/base.css"))
(type "text/css"))))
(block: morehead)) ; ... etc
(Continue reading)
By the way, to anyone interested in Scheme-based HTML template languages... I'm imminently releasing "html-template.scm", a new HTML template language implementation that does a lot of syntax-checking and formatting at Scheme syntax transformation time. (It actually works already. I just need 'a few hours' to finish documentation and herd the 4 interdependent packages into PLaneT.) Eddie Sullivan wrote at 04/30/2008 08:02 PM: > Well, here's the scenario I had in mind when I originally posed the question about class variables. I've since come up with a way to accomplish this without using classes at all, so this may be a moot point, but here it is. > > My idea was an x-expression based template library, where each template was enclosed in a class. [...] _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-scheme
Indeed; thank you for pointing that out.
After further thought, I came up with the following alternative solution last night (posted together with
the evaluation result):
--
(define nil '())
;Value: nil
(define (for-each proc items)
(if (null? items)
nil
(cond ((or (proc (car items)) #t) (for-each proc (cdr items))))))
;Value: for-each
(for-each (lambda (x) (newline) (display x) nil) (list 1 2 3))
1
2
3
;Value: ()
--
This doesn't use "begin", captures "for-each" in a single procedure, ignores the result of "(proc (car
items))", and uses side-effects.
Benjamin L. Russell
--- On Wed, 4/30/08, Jos Koot <jos.koot@...> wrote:
(Continue reading)
Something similar also happens to me nearly every time I try to download anything from pre.plt-scheme.org. It only works like once every 20 times. It's been like this for a while; I always thought the problem was on my end. It blasts the first few hundred Kb then the transfer rate just drops to 0. I don't get "Connection reset by peer" and the connection doesn't seem to be lost because wget's ETA keeps going up. $ wget http://pre.plt-scheme.org/installers/plt-3.99.0.23-bin-i386-linux-ubuntu-feisty.sh --01:12:34-- http://pre.plt-scheme.org/installers/plt-3.99.0.23-bin-i386-linux-ubuntu-feisty.sh => `plt-3.99.0.23-bin-i386-linux-ubuntu-feisty.sh' Resolving pre.plt-scheme.org... 129.10.115.117 Connecting to pre.plt-scheme.org|129.10.115.117|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 31,730,046 (30M) [application/x-sh] 1% [ ] 338,594 --(Continue reading).--K/s ETA 12:45:56 On Wed, 2008-04-30 at 18:17 -0400, Tom Schouten wrote: > hello, > > i'm not sure if this is the right spot to report it, but there seems to be a > problem with the web server hosting pre.plt-scheme.org > > i get connection resets when downloading the nightly builds.. > this has been going on for a while. the first time i remember this happening > was dowloading 3.99.0.10 on 2008-02-11 > > tom <at> klimop:~$ wget http://pre.plt-scheme.org/installers/full-3.99.0.23-bin-i386-linux-ubuntu.sh > --21:07:34-- http://pre.plt-scheme.org/installers/full-3.99.0.23-bin-i386-linux-ubuntu.sh > => `full-3.99.0.23-bin-i386-linux-ubuntu.sh'
Scheme UK is back on!! The next meeting for the Scheme UK user's group will be held on Wednesday, 28 May from 7pm till we leave for the pub. The meeting will take place at the offices of LShift(see http://www.lshift.net/contact.html for directions). Dave Griffiths: "Fluxus: Scheme Livecoding" Livecoding is the name given to improvised programming, usually in front of an audience, with screen projection to allow viewers to connect the construction of a program along with it's audio/visual/olfactory output. Fluxus is a rapid prototyping, livecoding and playing/learning environment for 3D graphics and games. It extends PLT Scheme with graphical commands and can be used within it's own livecoding environment or from within the DrScheme IDE. Date: 28 May Time: 7:00pm Venue: LShift Ltd Hoxton Point 1st Floor Office 6 Rufus Street London N1 6PE Map: http://www.lshift.net/contact(Continue reading)
... and useful. -- Matthias On Apr 30, 2008, at 4:55 PM, Robby Findler wrote: > Because one mark will clobber another if their corresponding > with-continuation-mark expressions are in tail-position wrt to each > other (indeed, that is the magic property that makes > with-continuation-mark primitive). > > Robby > > On Wed, Apr 30, 2008 at 3:27 PM, John Leuner > <jewel@...> wrote: >> Why does the output differ for these two cases: >> >> mzscheme -t >> test.ss >> Welcome to MzScheme v372 [3m], Copyright (c) 2004-2007 PLT Scheme >> Inc. >> (4 2) >> (4) >> >> John Leuner >> >> >> _________________________________________________ >> For list-related administrative tasks: >> http://list.cs.brown.edu/mailman/listinfo/plt-scheme >>(Continue reading)
Yes, this scenario makes sense in principle. No, I wouldn't use Scheme classes to do templates UNLESS the number of defaults is large and yet overriding a few of them at a time is needed. Even then, I'd consider keyword arguments with default values instead to do what you want to do. And also see Neil's answer. -- Matthias On Apr 30, 2008, at 8:02 PM, Eddie Sullivan wrote: > Well, here's the scenario I had in mind when I originally posed the > question about class variables. I've since come up with a way to > accomplish this without using classes at all, so this may be a moot > point, but here it is. > > My idea was an x-expression based template library, where each > template was enclosed in a class. The concept was based on some > existing text templating languages, where a template can contain > "blocks" that a derived template can override, and "parameters" > that can be set on a per-instance basis. In this case the template > expression would be associated with the class itself, while the > parameter values would be associated with an instance. > > I wanted a syntax where default block and parameter values could be > specified in-line in the template rather than as default parameters > to a function. And I wanted to be able to nest blocks.(Continue reading)
PLT Scheme's R6RS is now (in SVN) backed by a minimally competent test
suite --- and there are many fewer bugs than there were a week ago.
The test suite is in
collects/tests/r6rs
Also, as of a week or two ago, the R6RS document is wired into to the
PLT documentation. For example, running DrScheme's Check Syntax on
#!r6rs
(import (rnrs))
cons
provides a link from `cons' to the R6RS description of `cons'.
Known non-conformance with the standard in the current implementation:
* When `guard' catches an exception that no clause matches, the
exception is re-`raise'ed without restoring the continuation to the
one that raised the exception.
This difference can be made visible using `dynamic-wind'. According
to R6RS, the following program should print "in" and "out" twice,
but each prints once using PLT Scheme:
(guard (exn [(equal? exn 5) 'five])
(guard (exn [(equal? exn 6) 'six])
(dynamic-wind
(lambda () (display "in") (newline))
(lambda () (raise 5))
(Continue reading)
Hi, I'm trying to use the Framework (to select a folder), but I'm
having trouble getting the args right; I think I'm doing the minimum
sufficient to get a 'select files' dialog, but I'm getting a contrat
error that I don't quite understand - it doesn't seems to match the
contract in the manual.
Can anyone make any suggestions as to what I'm doing wrong?
[I'm using 3.99.0.23 [3m], built from source and running on Eee Xandros(debian)]
> (finder:common-get-file-list
#f
"get-folder"
#f
"not right"
#f)
. framework broke the contract
(->*
()
((or/c false/c path?)
string?
(or/c false/c byte-regexp?)
string?
(or/c
false/c
(is-a?/c interface:top-level-window<%>)))
(or/c (listof path?) false/c))
on finder:common-get-file-list; expected <(or/c (listof path?)
false/c)>, given: #<void>
>
(Continue reading)
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