Re: PSP

From: Benjamin Johnston (superhero_at_benjaminjohnston.com.au)
Date: 03/20/04 

Date: Sat, 20 Mar 2004 15:23:25 +1000

Oh, sorry... I just noticed the post from Oskar Bartenstein, in which we
were referred to the following document that explained MINERVA's syntax:
http://www.ifcomputer.co.jp/inap/inap2001/program/inap_bartenstein.ps

I take back my comment about it being low level (apparently the first
section isn't necessary) -- however, in my opinion, it doesn't really look
like Prolog programming.

But, on the other hand, none of the methods that I have seen or suggested
really allow for the possibility of writing webpages in a recursive manner
(with the exception of MINERVA - to a certain extent).

-Benjamin Johnston

"Benjamin Johnston" <superhero@benjaminjohnston.com.au> wrote in message
news:405bcb31$0$22512$5a62ac22@freenews.iinet.net.au...
>
> Okay, I'd be interested in your opinions on syntax of PSP...
>
> %%%%%%%%%%%%%%%
>
> I am now aware of four syntaxes:
> - Suciu and Pusztai
> - My own
> - Jan Wielemaker from SWI-Prolog (I haven't seen this code, however)
> - MINERVA Prolog, has MSS (but I can't find what that stands for)
>
> %%%%%%%%%%%%%%%
> % Suciu and Pusztai
> %%%%%%%%%%%%%%%
>
> Suciu and Pusztai,
>
http://conference.iasi.roedu.net/site/conference/papers/SUCIU_A-Prolog_Serve
> r_Pages.pdf
> used a syntax like this:
>
> <html>
> <head><title>Hello World example</title></head>
> <body>
> <?psp
> msg('Hello, World!').
> ?- msg(X),write(X).
> ?>
> </body>
> </html>
>
> I quite like this because it allows clauses to be defined, and queries
> submitted in the one document. Furthermore, if a query fails, it does not
> cause the entire page to "fail". On the downside, however, it doesn't
really
> look like it allows the programmer to directly mix the Prolog and HTML.
>
> %%%%%%%%%%%%%%%
> % My own
> %%%%%%%%%%%%%%%
>
> I experimented with many possibilities, but in my work I settled on the
idea
> that a PSP page is a query. So I had code like this:
>
> <html>
> <head><title>Hello World example</title>
> </head>
> <body>
> <?, X is 3 + 2, ?>
> Hi, the sum of 3 and 2 comes to <?= X ?>
>
> The members of my family are:<br>
> <?, forall(
> member(Person, ['ben','michael','sue','graham']),
> ?> <b><?= Person?></b><br> <?
> ),?>
> </pre>
> </body>
> </html>
>
> In other words, each PSP page was a single query - the parser basically
just
> replaced the HTML sections with writes, so that:
> hello <?, X=1, ?> X is equal to <?= X ?>
> would be translated into the following query,
> write('hello '), X = 1, (write('X is equal to'), write(X)).
>
> Predicates could be defined by the user because every .pl file in the
> current directory was automatically consulted on the webserver startup.
>
> The thing that I like about my approach is that it quite easy and natural
to
> produce fairly complex page layouts -- and that it works in a way that is
> very similar to the other server-pages technologies. The downside is that
> there is a greater need to be careful about coping with failure - because
if
> a particular subclause fails then the bottom of the page is likely to be
> chopped off. I don't think this is too big a deal, however, because this
is
> exactly the same issue that you need to consider when writing any old
Prolog
> predicate. Use of things that always succeed (such as forall) also prevent
> that from happenning. Another downside is that predicates cannot be
defined
> in-line --- however, I don't see any reason that I couldn't extend the
> syntax to include a <?prolog ?> or <?psp ?> tag that allows predicates to
be
> defined.
>
> %%%%%%%%%%%%%%%
> % Jan Wielemaker
> %%%%%%%%%%%%%%%
>
> As far as I can tell, Jan's code is not available.
>
> %%%%%%%%%%%%%%%
> % MINERVA
> %%%%%%%%%%%%%%%
>
> I could only find one sample .mss file in the MINERVA evaluation (I can't
> seem to find any online discussion of it, or mention of it in the
> documentation). But, the basic idea appears to be that you write something
> like a Java servlet in Prolog. It appears that MINERVA also has a special
> syntax to simplify development.
>
> I don't want to quote MINVERA's sample file in full -- you can download a
> free trial edition if you're interested. But, it looks like an .mss file
> consists of the following parts:
> <%!
> a set of prolog predicates to define how to respond to a particular
query --
> specifically taking POST/GET requests, and then appropriately "invoking"
the
> next "function" to handle it.
> in this case we might have an clause that says (sample copied directly
from
> MINVERA's file):
> select_method(_, Request, Response) :- !,
> response_setContentType(Response, 'text/html'),
> response_getWriter(Response, Writer),
> request_getContentType(Request, ContentType),
> show_error(Writer, ContentType).
> %>
>
> <%@ function show_error(ContentType) %>
> <html>
> some html content can go here
> </html>
> <% end %>
>
> <%@ function show_content(Request, MultipartRequest) %>
> <html>
> <body>
> <%@ include show_data(Request) %>
> <%@ include show_parts(MultipartRequest) %>
> </body>
> </html>
> <% end %>
>
> <%@ function show_data(Request) %>
> here's an in-line display: <%= request_getMethod(Request) %><br>
> <% end %>
>
> <%@ function show_parts(Request) %>
> <% loop multipart_element(Request, Element) %>
> <%@ include show_element(Request, Element) %>
> <% end %>
> <% end %>
>
> and so on...
>
> The advantage of this format, appears to be first and foremost a closer
> relationship to the underlying mechanisms themselves. It appears to be
more
> like what Java Servlets are to Java, but for Prolog. Of course, the
downside
> is that it looks like a lot of effort if all you really want to do is
> produce a simple website from a bit of Prolog.
>
> %%%%%%%%%%%%%%%
>
> I think I prefer my single query technique, but I like the way that Suciu
> and Pusztai allowed for predicates to be defined within the file. Maybe
the
> hybrid approach with <?prolog ?> or <?psp ?> defining the compile-time
tasks
> (that cannot generate input) and the single query approach is the best
> combination.
>
> Any thoughts?
>
> -Benjamin Johnston
>
> > Jan Wielemaker wrote:
> > <snipped>
> > > The SWI-Prolog application database (available from the website) runs
> > > in something I also called PSP (obvious name :-). I never published
> > > the code though and I don't think it is in a state where it is worth
> > > publishing :-)
> >
> > And here's yet another "Prolog Server Pages" implementation:
> >
>
http://conference.iasi.roedu.net/site/conference/papers/SUCIU_A-Prolog_Serve
> r_Pages.pdf
> > or in Google's HTML format:
> >
>
http://216.239.41.104/search?q=cache:CZQGjuYJzS8J:conference.iasi.roedu.net/
>
site/conference/papers/SUCIU_A-Prolog_Server_Pages.pdf+mod_psp+Prolog&hl=en&
> ie=UTF-8
>
>

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