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yap-6.3/packages/xml/xml_driver.pl

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