144 lines
5.7 KiB
Prolog
144 lines
5.7 KiB
Prolog
/* xml_driver.pl : Contains xml_parse/[2,3] a bi-directional XML parser written in
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* Prolog.
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*
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* Copyright (C) 2001-2005 Binding Time Limited
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* Copyright (C) 2005-2011 John Fletcher
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*
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* Current Release: $Revision: 3.3 $
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*
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* TERMS AND CONDITIONS:
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*
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* This program is offered free of charge, as unsupported source code. You may
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* use it, copy it, distribute it, modify it or sell it without restriction,
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* but entirely at your own risk.
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*/
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/** @pred xml_parse( {+Controls}, +?Chars, ?+Document )
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*
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* parses Chars to/from a data
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* structure of the form xml(<atts>, <content>). <atts> is a list of
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* <atom>=<string> attributes from the (possibly implicit) XML signature of the
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* document. <content> is a (possibly empty) list comprising occurrences of
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* ~~~
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* pcdata(<string>) : Text
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* comment(<string>) : An xml comment;
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* element(<tag>,<atts>,<content>) : <tag>..</tag> encloses <content>
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* : <tag /> if empty
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* instructions(<atom>, <string>) : Processing <? <atom> <params> ?>"
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* cdata( <string> ) : <![CDATA[ <string> ]]>
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* doctype(<atom>, <doctype id>) : DTD <!DOCTYPE .. >
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* ~~~~
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* The conversions are not completely symmetrical, in that weaker XML is
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* accepted than can be generated. Specifically, in-bound (Chars -> Document)
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* does not require strictly well-formed XML. Document is instantiated to the
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* term malformed(Attributes, Content) if Chars does not represent well-formed
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* XML. The Content of a malformed/2 structure can contain:
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*
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* unparsed( <string> ) : Text which has not been parsed
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* out_of_context( <tag> ) : <tag> is not closed
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*
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* in addition to the standard term types.
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*
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* Out-bound (Document -> Chars) parsing _does_ require that Document defines
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* strictly well-formed XML. If an error is detected a 'domain' exception is
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* raised.
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*
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* The domain exception will attempt to identify the particular sub-term in
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* error and the message will show a list of its ancestor elements in the form
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* <tag>{(id)}* where <id> is the value of any attribute _named_ id.
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*
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* At this release, the Controls applying to in-bound (Chars -> Document)
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* parsing are:
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*
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* extended_characters(<bool>) : Use the extended character
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* : entities for XHTML (default true)
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*
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* format(<bool>) : Strip layouts when no character data
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* : appears between elements.
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* : (default true)
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*
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* remove_attribute_prefixes(<bool>) : Remove namespace prefixes from
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* : attributes when it's the same as the
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* : prefix of the parent element
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* : (default false).
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*
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* allow_ampersand(<bool>) : Allow unescaped ampersand
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* : characters (&) to occur in PCDATA.
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* : (default false).
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*
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* [<bool> is one of 'true' or 'false']
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*
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* For out-bound (Document -> Chars) parsing, the only available option is:
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*
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* format(<Bool>) : Indent the element content
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* : (default true)
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*
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* Different DCGs for input and output are used because input parsing is
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* more flexible than output parsing. Errors in input are recorded as part
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* of the data structure. Output parsing throws an exception if the document
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* is not well-formed, diagnosis tries to identify the specific culprit term.
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*/
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:- module( xml_driver, [xml_parse/2,
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xml_parse/3,
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document_to_xml/3,
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xml_subterm/2
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]).
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xml_parse( Chars, Document ) :-
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xml_parse( [], Chars, Document ).
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xml_parse( Controls, Chars, Document ) :-
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( ground( Chars ) ->
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xml_to_document( Controls, Chars, Document )
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; otherwise ->
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document_to_xml( Controls, Document, Chars )
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).
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document_to_xml( Controls, Document, Chars ) :-
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( member( format(false), Controls ) ->
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Format = false
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; otherwise ->
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Format = true
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),
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( ground( Document ),
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document_generation(Format, Document, Chars0, [] ) ->
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Chars = Chars0
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; otherwise ->
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xml_fault( Document, [], Culprit, Path, Message ),
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xml_exception( Message, Document, Culprit, Path )
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).
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/** @pred xml_subterm( +XMLTerm, ?Subterm )
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*
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* unifies Subterm with a sub-term of Term.
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* Note that XMLTerm is a sub-term of itself.
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*/
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xml_subterm( Term, Term ).
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xml_subterm( xml(_Attributes, Content), Term ) :-
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xml_subterm( Content, Term ).
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xml_subterm( [H|T], Term ) :-
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( xml_subterm( H, Term )
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; xml_subterm( T, Term )
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).
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xml_subterm( element(_Name,_Attributes,Content), Term ) :-
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xml_subterm( Content, Term ).
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xml_subterm( namespace(_URI,_Prefix,Content), Term ) :-
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xml_subterm( Content, Term ).
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/* xml is intended to be a rather modular module: it should be easy to
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* build a program that can output XML, but not read it, or vice versa.
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* Similarly, you may be happy to dispense with diagnosis once you are
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* sure that your code will only try to make valid calls to xml_parse/2.
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*
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* It is intended that the code should be very portable too. Clearly,
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* some small changes will be needed between platforms, but these should
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* be limited to xml_utilities. xml_utilities contains most of the shared
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* code and most of the potentially non-portable code.
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*/
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:- ensure_loaded( xml_acquisition ).
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:- ensure_loaded( xml_diagnosis ).
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:- ensure_loaded( xml_generation ).
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:- ensure_loaded( xml_pp ).
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:- ensure_loaded( xml_utilities ).
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