Serve a web-page

In this lesson we create a web-page that shows locations on a map. We give a skeleton for the code that can display Google maps decorated with markers below. Please create a new file with the content below. This file defines a new module (map), which imports the web-server infrastructure as well as our previously created reasoning module. It does not provide any exports because its functionality (the predicate map/1) is called from the web-server based on the http_handler/3 declaration.

:- module(map, []).
                                % Web-server libraries
:- use_module(library(http/html_write)).
:- use_module(library(http/http_dispatch)).
:- use_module(library(http/http_parameters)).
                                % Pirates package Google map interface
:- use_module(components(gmap)).
                                % Import our query predicates
:- use_module(demo).

% Bind /map to the predicate map/1

:- http_handler('/map', map, []).

% The implementation of map/1

map(Request) :-
                        [ lat1(Lat1, [float]),
                          lon1(Lon1, [float]),
                          lat2(Lat2, [float]),
                          lon2(Lon2, [float])

        % ****

        reply_html_page(title('Piracy events'),
                        [ \gmap(Points)

The predicate reply_html_page/2 generates an HTML page from terms and calls to grammar rules. The rule gmap//1 emits an HTML page with embedded JavaScript that opens Google Maps. Creating HTML from Prolog is subject of the [[Prolog web-service HOWTO][[]].


  1. Complete the code above to show piracy events in the given bounding box on the map. You do this by replacing % *** above with calls that produce a list of point(Lat, Lon) terms from the given parameters. You can use the predicates you exported from and combine them using findall/3 to create a list of point-terms. Test the page using the following queries.

You are now ready to do more exercises.

See also
- Tutorial index
- Prolog web-service HOWTO