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Re: [Erlyaws-list] Yaws extension capabilities (was: status report)
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From: Mikael K. <mik...@cr...> - 2002-11-08 15:21:06
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fredag 08 november 2002 15:12 skrev Claes Wikstrom:
> > Another use would be to manage an XSLT tranformation for XML file, an=
d
> > various things like that.
>
> Mikke ??
Ok you asked for it, long reply warning.
(If you think it is useful you could add it to the yaws examples maybe)
I have been playing around, not with pure XSLT, but with an XSLT lookalik=
e in=20
pure Erlang, why walk over the bridge for water :-). (For pure XSLT there=
are
adapters to the Sablotron C++ transformer available for inets so I guess =
these
could be adapted for yaws.)
I also get a feeling that using the pattern match in Erlang for template =
match=20
can give *excellent* performance. Still only a feeling though.....
Since both Erlang and XSLT are kind of functional languages the basic thi=
ngs=20
map rather well. I give you an example of using xmerl (by Ulf Wiger) and =
yaws=20
together for "on the fly" transform.
Basically xmerl parses an xml string/file and returns a record of:
-record(xmlElement, {
=09=09 name,
=09=09 parents =3D [],
=09=09 pos,
=09=09 attributes =3D [],
=09=09 content =3D [],
=09=09 language =3D [],
=09=09 expanded_name =3D [],
=09=09 nsinfo =3D [],=09% {Prefix, Local} | []
=09=09 namespace =3D #xmlNamespace{}
=09=09 }).
Were content is a mixed list of yet other xmlElement records and/or xmlTe=
xt=20
(or other node types). XSLT also makes use of XPath which is also impleme=
nted=20
in xmerl.
Example of one of the first XSLT sheets I picked from "XSLT 2nd Edition" =
,=20
Michael Kay, WROX:
Original stylesheet:
<xsl:stylesheet
xmlns:xsl=3D"http://www.w3.org/1999/XSL/Transform"
version=3D"1.0">
<xsl:template match=3D"poem">
<html>
<head>
<title><xsl:value-of select=3D"title" /></title>
</head>
<body>
<xsl:apply-templates select=3D"title" />
<xsl:apply-templates select=3D"author" />
<xsl:apply-templates select=3D"stanza" />
<xsl:apply-templates select=3D"date" />
</body>
</html> =20
</xsl:template>
<xsl:template match=3D"title">
<div align=3D"center"><h1><xsl:value-of select=3D"." /></h1></div>
</xsl:template>
<xsl:template match=3D"author">
<div align=3D"center"><h2>By <xsl:value-of select=3D"." /></h2></div>
</xsl:template>
<xsl:template match=3D"date">
<p><i><xsl:value-of select=3D"." /></i></p>
</xsl:template>
<xsl:template match=3D"stanza">
<p><xsl:apply-templates select=3D"line" /></p>
</xsl:template>
<xsl:template match=3D"line">
<xsl:if test=3D"position() mod 2 =3D 0">  </xsl:if>
<xsl:value-of select=3D"." /><br />
</xsl:template>
</xsl:stylesheet>
-------------------------------------------------------------------------=
----------------
yaws xsl transform script:
<erl>
-include("/usr/local/lib/erlang/lib/xmerl-0.18/inc/xmerl.hrl").
-import(xserl, [ xslapply/2, value_of/1, select/2, foldxml/3 ]).
process_xml(Doc)->
=09template(Doc).
template(E =3D #xmlElement{name=3D'poem'})->
[ "<html>"
"<head>"
"<title>", value_of(select("title",E)), "</title>"
"</head>"
"<body>",
xslapply( fun template/1, select("title", E)),
%% lists:map can be called instead of xslapply when you pull with s=
elect
lists:map( fun template/1, select("author", E)),
xslapply( fun template/1, select("stanza", E)),
xslapply( fun template/1, select("date", E)),
"</body>"
"</html>" ];
template(E =3D #xmlElement{name=3D'title'}) ->
["<div align=3D\"center\"><h1>",=20
value_of(select(".", E)),
"</h1></div>"];
template(E =3D #xmlElement{name=3D'author'}) ->
["<div align=3D\"center\"><h2>By ",
%% value_of(select(".", E)), The one below does the same thing
%% but faster
value_of(E#xmlElement.content),=20
"</h2></div>"];
template(E =3D #xmlElement{name=3D'date'}) ->
["<p><i>", value_of(select(".", E)), "</i></p>"];
template(E =3D #xmlElement{name=3D'stanza'}) ->
{Lines,LineNo} =3D lists:mapfoldl(fun template_pos/2, 1, select("line=
", E)),
["<p>", Lines, "</p>"].
%% Since all values are pulled and all tags are processed, the default
%% rules do not need invokation.
%%=20
%% template(E)->
%% built_in_rules( fun template/1, E).
indent_line(0)->"  ";
indent_line(_)->"".
template_pos(E =3D #xmlElement{name=3D'line'}, P) ->
{[indent_line(P rem 2), value_of(E#xmlElement.content), "<br />"], P =
+ 1=20
}.
%% template_pos(E, P)->=20
%% {built_in_rules( fun template/1, E), P + 1}. =20
%% Not necessary here as template_pos/2 only is called
%% for line children, but good practice for general case
%% ---------------- yaws stuff -------------------------
process_doc(A, [{doc,Docname}])->
case xmerl_scan:file(A#arg.docroot ++ "/" ++ Docname,
=09=09=09 [{fetch_fun, fun(DTDSpec,S) -> {ok,S} end},
=09=09=09 {space,normalize}]) of
=09{error, Result} ->
=09 io:fwrite("Error ~p~n", [Result]),
=09 perr();
=09{B,_} ->
=09 C =3D process_xml(B),
=09 {content,"text/html",C}
end;
process_doc(A, _) ->
perr().
perr()->
{ehtml,{html,[],
=09 [
=09 {head,[],{title,[],"Error"}},
=09 {body,[],[
=09=09 {h1,[],"Error"},
=09=09 {p,[],"No or Erroneous Document name"}
=09=09 ]}
=09 ]
=09 }
}.
=20
out(A) ->=20
process_doc(A, yaws_api:parse_query(A)).
</erl>
------------------------------
Functions used:
xslapply(Fun, EList) when list(EList) ->
lists:map( Fun, EList);
xslapply(Fun, E =3D #xmlElement{})->
lists:map( Fun, E#xmlElement.content).
%% value_of concatenates all text nodes within the tree
value_of(E)->
lists:reverse(foldxml(fun value_of1/2, [], E)).
value_of1(#xmlText{}=3DT1, Accu)->
[T1#xmlText.value|Accu];
value_of1(E, Accu) ->
Accu.
%% xmerl_xpath does the job.
select(Str,E)->
xmerl_xpath:string(Str,E).
%% The default fallback behaviour, template funs should
%% end with:
%% template(E)->built_in_rules(fun template/1, E).
built_in_rules(Fun, E =3D #xmlElement{})->
lists:map(Fun, E#xmlElement.content);
built_in_rules(Fun, E =3D #xmlText{}) ->
E#xmlText.value;
built_in_rules(Fun, E =3D #xmlAttribute{}) ->
E#xmlAttribute.value;
built_in_rules(Fun, E) ->[].
%% foldxml
%% Fun is fun(#xmlElement, OldAccu) -> NewAccu
=20
foldxml(Fun, Accu0, #xmlElement{content=3DC}=3DE) ->
Accu1 =3D Fun(E, Accu0),
foldxml(Fun, Accu1, C);
foldxml(Fun, Accu, List) when list(List) ->
AFun =3D fun(E,A) -> foldxml(Fun, A, E) end,
lists:foldl(AFun, Accu, List);
foldxml(Fun, Accu, E) ->
Fun(E, Accu).
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