Grammar Hack Example for Digua

CSS.g

// intialization section
grammar CSS21;

options
{
	backtrack=true;
	memoize=true;
	superClass=DiguaParser;
}

@lexer::header {
package net.sf.digua;
}

@parser::header {
package net.sf.digua;
}

@parser::members {
	private CSS21Processor getCSSProcessor() {
		return (CSS21Processor)getProcessor();
	}
}

// additional stuff here

term
	: unaryOperator?
		(
			  NUMBER
			| PERCENTAGE
			| LENGTH
			| EMS
			| EXS
			| ANGLE
			| TIME
			| FREQ
		)
	| possibleColor=STRING
	{
	    $possibleColor.setText(getCSSProcessor()
		.minimizeColor($possibleColor.text));
	}
	| IDENT (	// Function
				LPAREN expr RPAREN
			)?
	| URI
	| hexColor
	;
	
hexColor
	: hexColorName=HASH
	{
	    $hexColorName.setText(getCSSProcessor()
		.minimizeColor($hexColorName.text));
	}		
	;

CSS21Processor.java

	protected String minimizeColor(String value) {
		if (minimizeColors) {
			try {
				return HTMLColor.getMinHTML(value);
			} catch (IllegalArgumentException exc) {
			}
		} 
		return value;
	}

HTMLColor.java

    /** Given an HTML color returns the minimum size string
     * representing that color. 
     * @throws IllegalArgumentException if the color name is 
     * not recognized or the value contains invalid digits or 
     * the number of digits is not 3 or 6.
     */
    public static String getMinHTML(String value) {
    	if (value.length() <= 3)
    		return value;
    	Color c = forName(value);
    	HTMLColor hc = valueOf(c);
    	if (hc != null && hc.name().length() 
			< value.length())
    		value = hc.name();

    	if (value.length() <= 3)
    		return value;
    	String rgb = toHex(c.getRed()) + toHex(c.getGreen()) 
		+ toHex(c.getBlue());

    	if (rgb.charAt(0) == rgb.charAt(1) && 
			rgb.charAt(2) == rgb.charAt(3) && 
			rgb.charAt(4) == rgb.charAt(5)) {
    		rgb = new StringBuilder().append(rgb.charAt(0))
			.append(rgb.charAt(2))
			.append(rgb.charAt(4)).toString();
    	}
    	if (rgb.length() < value.length())
    		value = "#" + rgb;
    	return value;
    }