REST APIs are a commonly used principle to make functionality available on the web. Given a REST API, web applications are developed as client side JavaScript programs.

A REST API server is constructed upon the SWI-Prolog HTTP server provided by library(http/http_server). HTTP locations (REST endpoints) are registered using http_handler/3. An example registration is here:

:- http_handler(root(user/User), user(Method, User),
                [ method(Method),
                  methods([get,post,put])
                ]).

user(get, User, Request) :-
    ...
user(post, User, Request) :-
    ...

Often, data is exchanged as JSON. SWI-Prolog provides good support for representing JSON using dicts and strings as well as full IEEE float support including NaN and Inf. A typical handler is written as below. See http_read_json_dict/2 and reply_json_dict/1 for details.

my_handler(Request) :-
    http_read_json_dict(Request, In),
        <do your computation>(In, Out),
        reply_json_dict(Out).

See also

- library(http/http_cors) to deal with CORS headers.