html
This library provides predicates for generating HTML content using either HTML 5 or XHTML 1.1 formats from a term representation. The library performs minimal validation, checking only that all elements are valid. No attempt is made to generate nicely indented output.
Normal elements are represented using a compound term with one argument
(the element content) or two arguments (the element attributes
represented by a list of Key=Value
or Key-Value
pairs and the
element content). The element content can be another element or a list
of elements. For example:
ol([type-a], [li(foo), li(bar), li(baz)])
The two exceptions are the pre
or code
elements whose content is
never interpreted as an element or a list of elements. For example, the
fragment:
pre([foo,bar,baz])
is translated to:
<pre>
[foo,bar,baz]
</pre>
Void elements are represented using a compound term with one argument,
the (possibly empty) list of attributes represented by a list of
Key=Value
or Key-Value
pairs. For example:
hr([class-separator])
Atomic arguments of the compound terms are interpreted as element
content. Non atomic element content can be represented as a quoted atom
or by using the pre
or code
elements as explained above.
This library is a work in progress.
API documentation
Open the ../../docs/library_index.html#html link in a web browser.
Loading
To load all entities in this library, load the loader.lgt
file:
| ?- logtalk_load(html(loader)).
Testing
To test this library predicates, load the tester.lgt
file:
| ?- logtalk_load(html(tester)).
Generating a HTML document
HTML documents can be generated from a compound term representation and written to a file or a stream. For example, assuming we want to generate a HTML 5 file:
| ?- html5::generate(
file('hello.html'),
html([lang=en], [head(title('Hello world!')), body(p('Bye!'))])
).
When the second argument is a html/1
or html/2
compound term, a
doctype is automatically written. If we prefer instead e.g. a XHTML
1.1 document, we use the xhtml11
object:
| ?- xhtml11::generate(
file('hello.html'),
html([lang=en], [head(title('Hello world!')), body(p('Bye!'))])
).
Generating a HTML fragment
It’s also possible to generate just a fragment of a (X)HTML document by
using a list of compound terms or a compound term for an element other
then html
. For example:
| ?- current_output(Stream),
html5::generate(stream(Stream), ul([li(foo), li(bar), li(baz)])).
<ul>
<li>
foo</li>
<li>
bar</li>
<li>
baz</li>
</ul>
Stream = ...
Working with callbacks to generate content
Often we need to programmatically generate HTML content from queries. In
other cases, we may have fixed content that we don’t want to keep
repeating (e.g. a navigation bar). The library supports a (::)/2
pseudo-element that sends a message to an object to retrieve content. As
an example, assume the following predicate definition in user
:
content(strong('Hello world!')).
This predicate can then be called from the HTML term representation. For example:
| ?- current_output(Stream),
html5::generate(stream(Stream), span(user::content)).
<span><strong>Hello world!</strong></span>
Stream = ...
Note that the callback always takes the form Object::Closure
where
Closure
is extended with a single argument (to be bound to the
generated content). More complex callbacks are possible by using lambda
expressions.
Working with custom elements
The html5
and xhtml11
objects recognize the same set of standard
HTML 5 normal and void elements and generate an error for non-standard
elements. If you need to generate HTML content containing custom
elements, define a new object that extends one of the library objects.
For example:
:- object(html5custom,
extends(html5)).
normal_element(foo, inline).
normal_element(bar, block).
normal_element(Name, Display) :-
^^normal_element(Name, Display).
:- end_object.