Kate: More on Indentation Scripting

My last blog was about the theory of how indentation works by using javascripts. Now we will look at a concrete example: a LISP-style indenter. (LISP indentation is easy, that's why it's a good example).
The rules:

• comments starting with ;;; always have indentation 0
• comments starting with ;; should be aligned with the next line
• comments starting with ; should only appear behind code, so they are simply ignored
• every '(' indents and every ')' unindents

lisp.js looks like this:

/** kate-script
 * name: LISP
 * license: LGPL
 * author: foo bar
 * version: 1
 * kate-version: 3.0
 * type: indentation
 */
// indent should be called when ; is pressed
triggerCharacters = ";";
function indent(line, indentWidth, ch)
{
    // special rules: ;;; -> indent 0
    //                ;;  -> align with next line, if possible
    //                ;   -> usually on the same line as code -> ignore
    textLine = document.line(line);
    if (textLine.search(/^\s*;;;/) != -1) {
        return 0;
    } else if (textLine.search(/^\s*;;/) != -1) {
        // try to align with the next line
        nextLine = document.nextNonEmptyLine(line + 1);
        if (nextLine != -1) {
            return document.firstVirtualColumn(nextLine);
        }
    }

    cursor = document.anchor(line, 0, '(');
    if (cursor) {
        return document.toVirtualColumn(cursor.line, cursor.column) + indentWidth;
    } else {
        return 0;
    }
}

The result:

;;; fib : number -> number
(define (fib n)
  (if (< n 2)
    1
    (+ (fib (- n 1)) (fib (- n 2)))))

As this indenter is scripted, everybody can adapt the style to the own needs.