New languages supported: JScript, VBScript, C, XML !
Outline
This is the first of a 2 articles serie. In this article, the techniques and ideas are discussed and a Javascript solution is given. In Part 2, a C#
solution is given.
Unfortunately for JScript
users, I will not update the JScript
code and focus on C#
only. :)
Introduction
Have you ever wondered how the CP team highlights the source code in their edited article ? I suppose it's not by hand and they must have some clever code to do it.
However, if you look around in the forums on the web, you will see that there are few if any who have this feature. Sad thing, because colored source code is much easier to read. In fact, it would be great to have source code in forums automatically colored with your favorite coloring scheme.
The last-but-not-least reason for writing this article was to learn regular expressions, javascript and DOM in one project.
The source code entirely written in JScript so it can be included server-side or client-side in your web pages.
The techniques used are:
- regular expressions
- XML DOM
- XSL transformation
- CSS style
When reading this article, I will assume that you have little knowledge of regular expressions, DOM and XSLT although I'm also a newbie in those 3 topics.
Live Demo
CP does not accept
script
or
form
tags in the article. To play with the live demo, download the "JScript" enabled page (see download section).
Transformation Overview
|
Parsing pipe |
All the boxes will be discussed in details in the next chapter. I will give here an short overview of the process.
First, a language syntax specification file is loaded (Language specification box). This specification is a plain xml file given by the users. In order to speed up things, preprocessing is made on this document (Preprocessing box).
Let us suppose for simplicity that we have the source code to colorize (Code box). Note that I will show how to apply the coloring to a whole html page later on. The parser, using the preprocessed syntax document, builds an XML document representing the parsed code (Parsing box). The technique used by the parser is to split up the code in a succession of nodes of different types: keyword, comment, litteral, etc...
At last, an XSTL transformation are applied to the parsed code document to render it to HTML and a CSS style is given to match the desired appearance.
Parsing Procedure
The philosophy used to build the parser is inspired from the Kate documentation (see [1]).
The code is considered as a succession of contexts. For example, in C++,
- keyword: if, else, while, etc...
- preprocessor instruction: #ifdef, ...
- literals: "..."
- line comment: // ...
- block comment: /* ... */
- and the rest.
For each context, we define rules that have 3 properties:
- a regular expression for matching a string
- the context of the text matched by the rule: attribute
- the context of the text following the rule: context
The rules have priority among them. For example, we will first look for a /* ... */ comment, then a // ... line comment, then litteral, etc...
When a rule is matched using a regular expression, the string matched by the rule is assigned with the attribute context, the current context is updated as context and the parsing continues. The diagram show the possible path between contexts. As one can see, some rule do not lead to a need context.
| |
Context dynamics |
Let me explain a bit the schema below. Consider that we are in the code
context. We are going to look for the first match of the code rules: ,
. Moreover, we have to take into account their priorities: a keyword is not really a keyword in a block of comment, so it has a lower priority. This task is easily and naturally done through regular expressions.
Once we find a match, we look for the rule that triggered that match (always following the priority of the rules). Therefore, pathological like is well parsed:
while is not considered as a keyword since it is in a comment.
Rules Available
There are 5 rules currently available:
- detect2chars: detects a pattern made of 2 characters.
- detectchar: detects a pattern made of 1 character.
- linecontinue: detects end of line
- keyword:detect a keyword out of a keyword family
- regexp:matches a regular expression.
regexp is by far the most powerful rule of all as all other rules are represented internally by regular expressions.
Language Specification
From the rules and context above, we derive an XML structure as described in the XSD schema below (I don't really understand xsd but .Net generates this nice diagram...)
|
Language specification schema. Click on the image to view it full size. |
I will breifly discuss the language specification file here. For more details, look at the xsd schema or at highlight.xml
specification file (for C++). Basically, you must define families of keywords, choose context and write the rule to pass from one to another.
Nodes
Name |
Type |
Parent Node |
Description |
highlight |
root |
none |
The root node |
needs-build |
A (optional) |
highlight |
"yes" if file needs preprocessing |
save-build |
A (optional***) |
highlight |
"yes" if file has to be saved after preprocessing |
keywordlists |
E |
highlight |
Node containing families of keywords as children |
keywordlist |
E |
keywordlist |
A family of keywords |
id |
A |
keywordlist |
String identifier |
pre |
A (optional) |
keywordlist |
Regular to append before keyword |
post |
A (optional) |
keywordlist |
Regular to append at the end of the keyword |
regexp |
A (optional*) |
keywordlist |
Regular expression matching the keyword family. Build by the preprocessor |
kw |
E |
keywordlist |
Text or CDATA node containing the keywords |
languages |
E |
highlight |
Node containing languages as children |
language |
E |
languages |
A language specification |
contexts |
E |
language |
A collection of context node |
default |
A |
contexts |
String identifying the default context |
context |
E |
contexts |
A context node containing rules as children |
id |
A |
context |
String identifier |
attribute |
A |
context |
The name of the node in which the context will be stored. |
detect2chars** |
E |
context |
Rule to dectect pair of characters. (ex: ) |
char |
A |
detect2chars |
First character of the pattern |
char1 |
A |
detect2chars |
Second character of the pattern |
detectchar** |
E |
context |
Rule to dectect one character. (ex: " ) |
char |
A |
detectchar |
character to match |
keyword** |
E |
context |
Rule to match a family of keywords |
family |
A |
keyword |
Family indentifier, must match /highlight/keywordlists/keyword[@id] |
regexp |
E |
context |
A regular expression to match |
expression |
A |
regexp |
the regular expression. |
Comments:
- *: this argument is optional at the condition that preprocessing takes place. The usual way to do is to always preprocess or to preprocess once with the "save-build" parameter set to "yes" so that the preprocessing is save. Note that if you modify the language syntax, you will have to re-preprocess.
- **: all those element have two other attributes:
attribute (optional) |
A |
a rule |
The name of the node in which the string match will be stored. If not set or equal to "hidden", no node is created. |
context |
A |
a rule |
The next context. |
- ***: Client-side javascript is not allowed to write files. Hence, this option aplies only to server-side execution.
Preprocessing
In the preprocessing phase, we are going to build the regular expressions that will be used later on to match the
rules. This section makes an extensive use of
regular expressions. As mentionned before, this is not a tutorial on regular expressions since I'm also a newbie in that topic. A tool that I have found to be
really useful is
Expresso (see [3]) a regular expression test machine.
Keyword Families
Building the keyword families regular expressions is straightforward. You just need to concatenate the keywords togetter using
|:
<keywordlist ...>
<kw>if</kw>
<kw>else</kw>
</keywordlist>
will be matched by
\b(if|else)\b
The generated regular expression is added as an attribute to the keywordlist node:
<keywordlist regexp="\b(if|else)\b">
<kw>if</kw>
<kw>else</kw>
</keywordlist>
When using libraries of function, it is usual to have a common function header, like for OpenGL:
glVertex2f, glPushMatrix(), etc...
You can skip the hassle of rewritting
gl
in all the
kw
items by using the attribute
pre
which takes a regular expression as a parameter:
<keywordlist pre="gl" ...>
<kw>Vertex2f</kw>
<kw>PushMatrix</kw>
</keywordlist>
will be matched by
\bgl(Vertex2f|PushMatrix)\b
You can also add regular expression after the keyword using
post
. Still working on our OpenGL example, there are some methods that have characters at the end to tell the type of parameters:
glCoord2f
: takes 2 floats,
glRaster3f
: takes 3 floats,
glVertex4v
: takes an array of floats of size 4
Using
post
and regular expression, we can match it easily:
<keywordlist pre="gl" post="[2-4]{1}(f|v){1}" ...>
<kw>Vertex</kw>
<kw>Raster</kw>
</keywordlist>
will be matched by
\bgl(Vertex2f|PushMatrix)[2-4]{1}(f|v){1}\b
String Literals
This is a little exercise on regular expression: How to match a literal string in C++? Remember that it must support \"
, end of line with \
.
My answer (remember I'm a newbie) is
"(.|\\"|\\\r\n)*?((\\\\)+"|[^\\]{1}")
I tested this expression on the following string:
"a simple string"
---
"a less \" simple string"
---
"a even less simple string \\"
---
"a double line\
string"
---
"a double line string does not work without
backslash"
---
"Mixing" string "can\"" become "tricky"
---
"Mixing \" nasty" string is \" even worst"
Contexts
The context regular expression is also build by concatenating the regular expression of the rules. The value is added as an attribute to the context node:
<context regexp="(...|...)">
Controlling if Preprocessing is Neccessary
It is possible to skip the preprocessing phase or to save the "preprocessed" language specification file. This is done by specifying the following parameters in the root node
highlight
Attribute |
Description |
Default |
need-build |
"yes" if needs preprocessing |
yes |
save-build |
"yes" if saving preprocessed language specification to disk |
no |
Javascript call
The preprocessing phase is done through the javascript method loadAndBuildSyntax
:
var sXMLSyntax = "highlight.xml";
var xmlDoc = loadAndBuildSyntax( loadXML( sXMLSyntax ) );
Parsing
We are going to use the language syntax above to build an XML tree out of the source code. This tree will be made out of successive
context nodes.
We can start parsing the string (pseudo-code below):
source = source code;
context = code;
regExp = context.regexp;
while( source.length > 0)
{
Here we follow the procedure:
- find first match of the contextrules
- store the source before the match
- find the rule that was matched
- process the rule parameters
match = regExp.execute( source );
if( !match)
{
addChildNode( context
source
break;
}
else
{
The source before the match has to be stored in a new node:
addChildNode( context, source before match);
We now have to find the rule that has matched. This is done by the method findRule
that returns the rule node. The rule is then processed using attribute and context parameters.
ruleNode = findRule( match );
if (ruleNode.attribute != "hidden")
addChildNode( attribute, match);
context=ruleNode.context;
regExp=context.regexp;
}
}
At the end of this method, we have build an XML tree containing the context. For example, consider the classic of the classic "Hello world" program below:
int main(int argc, char* argv[])
{
cout<<"Hello world";
return -1;
};
This sample is translated in the following xml structure:
<parsedcode lang="cpp" in-box="-1">
<reservedkeyword>int</reservedkeyword>
<code> main(</code>
<reservedkeyword>int</reservedkeyword>
<code> argc, >
Here is the specification of the resulting XML file:
Node Name |
Type |
Parent Node |
Description |
parsedcode |
root |
| Root node of document |
lang |
A |
parsedcode |
type of language: c, cpp, jscript, etc. |
in-box |
A |
parsedcode |
-1 if it should be enclosed in a pre tag, otherwize in code tag |
code |
E |
parsedcode |
non special source code |
and others... |
E |
parsedcode |
|
Javascript Call
The algorithm above is implemented in the applyRules
method:
applyRules( languageNode, contextNode, sCode, parsedCodeNode);
where
languageNode
is the current language node (XMLDOMNode
),
contextNode
is the start context node (XMLDOMNode
),
sCode
is the source code (String
),
parsedCodeNode
is the parent node of the parsed code (XMLDOMNode
)
XSLT Transformation
Once you have the XML representation of your code, you can basically do whatever you want with it using XSLT transformations.
Header
Every XSL file starts with some declarations and other standard options:
="1.0" ="ISO-8859-1"
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:output encoding="ISO-8859-1" indent="no" omit-xml-declaration="yes"/>
Since source code indenting has to be conserved, we disable automatic indenting and, also the xml declaration is omitted:
<xsl:output encoding="ISO-8859-1" indent="no" omit-xml-declaration="yes"/>
Basic Templates
<xsl:template match="cpp-linecomment">
<span class="cpp-comment">//<xsl:value-of select="text()"
disable-output-escaping="yes" /></span>
</xsl:template>
This template appies to the node cpp-linecomment
which corresponds to single line comment in C++.
We apply the CSS style to this node by encapsulating it in span
tags and by specifying the CSS class.
Moreovern, we do not want character escaping for that, so we use
<xsl:value-of select="text()" disable-output-escaping="yes" /></span>
The Parsedcode Template
It gets a little complicated here. As everybody knows, XSL quicly becomes really complicated once you want to do more advanced stylesheets. Below is the template for parsedcode
, it does simple thing but looks ugly:
Checks if in-box
parameter is true, if true create pre
tags, otherwize create code
tags.
<xsl:template match="parsedcode">
<xsl:choose>
<xsl:when test="@in-box[.=0]">
<xsl:element name="span">
<xsl:attribute name="class">cpp-inline</xsl:attribute>
<xsl:attribute name="lang">
<xsl:value-of select="@lang"/>
</xsl:attribute>
<xsl:apply-templates/>
</xsl:element>
</xsl:when>
<xsl:otherwise>
<xsl:element name="pre">
<xsl:attribute name="class">cpp-pre</xsl:attribute>
<xsl:attribute name="lang">
<xsl:value-of select="@lang"/>
</xsl:attribute>
<xsl:apply-templates/>
</xsl:element>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
Javascript Call
This is where you have to customize a bit the methods. The rendering is done in the method highlightCode
:
highlightCode( sLang, sRootTag, bInBox, sCode)
where
sLang
is a string identifying the language ( "cpp" for C++),
sRootTag
will the node name encapsulation the code. For example, pre
for boxed code, code
for inline code,
bInCode
a boolean set to true if in-box
has to be set to true.
sCode
is the source code
- it returns the modified code
The file names are hardcoded inside the highlightCode
method: hightlight.xml
for the language specification, highlight.xsl
for the stylesheet. In the article, the XML syntax is embed in a xml
tag and is simply accessed using the id
Applying Code Transformation to an Entire HTML Page.
So now you are wondering how to apply this transformation to an entire HTML page? Well surprisingly, this can be done in... 2 lines! In fact, there exist the method String::replace(regExp, replace)
that replaces the substring matching the regular expressions regExp
with replace
. The best part of the story is that replace
can be a function... So we just (almost) need to pass highlightCode
and we are done.
For example, we want to match the code enclosed in pre
tags:
var regExp=/<pre>(.|\n)*?<\/pre>/gim;
var sValue = sValue.replace( regExp,
function( $0 )
{
return highlightCode("cpp", "cpp",$0.substring( 5, $0.length-6 ));
}
);
In practice, some checking are made on the language name and all these computations are hidden in the replaceCode
method.
Using the Methods in your Web Wite
ASP Pages
To use the highlightin scheme in your ASP web site:
- Put the javascript code between script tags in an asp page:
<script language="javascript" runat="server">
...
</script>
- include this page where you need it
- modify the method
processAndHighlightCode
to suit your needs
- modify the method handleException to redirect the exception to the Response
- apply this method to the HTML code you want to modify
- update your
css
style with the corresponding classes.
Demonstration Application
The demonstration application is a hack of the CodeProject Article Helper. Type in code in pre
or code
to see the results.
Update History
Date |
Description |
02-20-2002 |
- Added demonstration in the article!
- Added new languages: JScript, VBScript, C, XML
- Now handling <pre lang="..."> bracketting: you can specify the language of the code.
loadAndBuildSyntax takes a DomDocument as parameter. You can call it like this: loadAndBuildSyntax( loadXML( sFileName ))
highlightCode takes one more argument: bInBox. |
02-17-2002 |
Minor changes in stylesheet |
02-14-2003 |
- Added
pre , post to the keyword rule <li> The text disapearing in <code> brackets is fixed. The bug was in processAndHighlightArcticle (bad function argument).</li> </ul> |
02-13-2003 |
Initial release. |
References