http package (only partially working)

packages/http/examples/calc.pl

@@ -0,0 +1,92 @@
+/*  $Id$
+
+    Part of SWI-Prolog
+
+    Author:        Jan Wielemaker
+    E-mail:        wielemak@science.uva.nl
+    WWW:           http://www.swi-prolog.org
+    Copyright (C): Public domain
+*/
+
+:- use_module(library('http/thread_httpd')).
+:- use_module(library('http/html_write')).
+:- use_module(library('http/http_session')).
+:- use_module(library('http/http_error')).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+This demo shows session state  management   in  a very simple calculator
+package. It also demonstrates the use of  the html_write library. To use
+it, start Prolog, load this file and run
+
+	?- server.
+
+Now direct your browser to http://localhost:3000/
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+server :-
+	server(3000, []).
+
+server(Port, Options) :-
+	http_server(reply,
+		    [ port(Port),
+		      timeout(20)
+		    | Options
+		    ]).
+
+reply(Request) :-
+	memberchk(path(Path), Request),
+	reply(Path, Request).
+
+reply(/, _Request) :-
+	http_session_retractall(formula(_)),
+	Formula = 0,
+	http_session_assert(formula(Formula)),
+	page(Formula).
+
+reply('/calc', Request) :-
+	memberchk(search(Search), Request),
+	memberchk(operation=Op, Search),
+	memberchk(value=AtomVal, Search),
+	atom_number(AtomVal, Val),
+	http_session_retract(formula(Formula0)),
+	debug(calc, 'Formula0 = ~w', [Formula0]),
+	Formula =.. [Op, Formula0, Val],
+	http_session_assert(formula(Formula)),
+	page(Formula).
+
+
+page(Formula) :-
+	reply_page('HTTP Session DEMO',
+		   [ h2('Simple session demo'),
+		     form([ action('/calc'),
+			    method('GET')
+			  ],
+			  table([align(center), border(1)],
+				[ tr(td(\formula(Formula))),
+				  tr(td([ \ops,
+					  input([ name(value) ]),
+					  input([ type(submit),
+						  value('Calc!')
+						])
+					]))
+				]))
+		   ]).
+
+formula(Formula) -->
+	{ sformat(S, '~w', [Formula]),
+	  Value is Formula
+	},
+	html([ S, ' = ', Value ]).
+
+ops -->
+	html(select(name(operation),
+		    [ option([selected], +),
+		      option([], -),
+		      option([], /),
+		      option([], *)
+		    ])).
+
+reply_page(Title, Content) :-
+	phrase(page(title(Title), Content), HTML),
+	format('Content-type: text/html~n~n'),
+	print_html(HTML).