Scryer Prolog documentation

Module sgml

:- use_module(library(sgml)).

Predicates for parsing HTML and XML documents.

Currently, two predicates are provided:

  • load_html(+Source, -Es, +Options)

  • load_xml(+Source, -Es, +Options)

These predicates parse HTML and XML documents, respectively.

Source must be one of:

  • a list of characters with the document contents

  • stream(S), specifying a stream S from which to read the content

  • file(Name), where Name is a list of characters specifying a file name.

Es is unified with the abstract syntax tree of the parsed document, represented as a list of elements where each is of the form:

  • a list of characters, representing text

  • element(Name, Attrs, Children)

    • Name, an atom, is the name of the tag

    • Attrs is a list of Key=Value pairs: Key is an atom, and Value is a list of characters

    • Children is a list of elements as specified here.

Currently, Options are ignored. In the future, more options may be provided to control parsing.


   ?- load_html("<html><head><title>Hello!</title></head></html>", Es, []).


      Es = [element(html,[],

library(xpath) provides convenient reasoning about parsed documents. For example, to fetch the title of the document above, we can use:

   ?- load_html("<html><head><title>Hello!</title></head></html>", Es, []),
      xpath(Es, //title(text), T).

Yielding T = "Hello!".

Use http_open/3 from library(http/http_open) to read answers from web servers via streams.