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    1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        jan@swi-prolog.org
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2024, SWI-Prolog Solutions b.v.
    7    All rights reserved.
    8
    9    Redistribution and use in source and binary forms, with or without
   10    modification, are permitted provided that the following conditions
   11    are met:
   12
   13    1. Redistributions of source code must retain the above copyright
   14       notice, this list of conditions and the following disclaimer.
   15
   16    2. Redistributions in binary form must reproduce the above copyright
   17       notice, this list of conditions and the following disclaimer in
   18       the documentation and/or other materials provided with the
   19       distribution.
   20
   21    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   22    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   23    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   24    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   25    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   26    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   27    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   28    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   29    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   31    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   32    POSSIBILITY OF SUCH DAMAGE.
   33*/
   34
   35:- module(htmx,
   36          [ reply_htmx/1,               % +HTML
   37            reply_htmx/2,               % +HTML, +Request
   38            htmx_oob//2                 % ++Id, :HTML
   39          ]).   40:- use_module(library(http/html_write)).

Support htmx.org

Quoted from htmx.org:

htmx gives you access to AJAX, CSS Transitions, WebSockets and Server Sent Events directly in HTML, using attributes, so you can build modern user interfaces with the simplicity and power of hypertext

The idea behind htmx is to allow adding attributes to any HTML element that cause an HTTP request. The HTTP response is typically a (short) HTML fragment that extends or replaces an element on the page. This allows us to program a most functionality interactive seen in modern web applications using the powerful SWI-Prolog HTML generation framework rather than having to write a JSON backend and accompanying JavaScript frontend that runs in the browser.

Below is a minimal, yet fully functional application

:- use_module(library(http/http_server)).
:- use_module(library(http/htmx)).
:- use_module(library(main)).

:- initialization(main, main).

main(_Argv) :-
    http_server([port(8080)]),
    thread_get_message(quit).

http:location(htmx, root(htmx), []).

:- http_handler(root(.), home, []).

home(_Request) :-
    reply_html_page(
        [ title('HTMX demo'),
          script(src('https://unpkg.com/htmx.org'), [])
        ],
        [ button([ 'hx-post'('/htmx/clicked'),
                   'hx-swap'('outerHTML')
                 ],
                 'Click me')
        ]).

:- http_handler(htmx(clicked), reply_htmx(\clicked), []).

clicked -->
    html('Thanks for clicking me!').

HTMX requires no dedicated support from the server. This library provides reply_htmx/1,2 to reply with a single HTML element rather than an entire page. Future versions of this library may provide some additional utility predicates. */

   99:- html_meta
  100    reply_htmx(html),
  101    reply_htmx(html, +),
  102    htmx_oob(+, html, ?, ?).
 reply_htmx(+HTML) is det
 reply_htmx(+HTML, +Request) is det
Reply a plain HTML element as opposed to a complete HTML page as created using reply_html_page/2,3. While reply_htmx/1 is to be used in a normal HTTP handler (route), reply_htmx/2 may be registered directly in the http_handler/3 declaration to deal with simple cases where we do not need the Request data.
  113reply_htmx(HTML) :-
  114    phrase(html(HTML), Tokens),
  115    format('Content-type: text/html~n~n', []),
  116    print_html(Tokens).
  117
  118reply_htmx(HTML, _Request) :-
  119    reply_htmx(HTML).
 htmx_oob(++Target, :HTML)// is det
Emit an htmx out-of-band element. HTML is used to swap the content of the DOM element with id Target.
  126htmx_oob(Target, HTML) -->
  127    html(div([id(Target), 'hx-swap-oob'(true)],
  128             HTML))