static class LBla extends LearnerImpl {
  static boolean debug;
  String inPattern, outPattern;

  public void processInOut(Object _in, Object _out) {
    String in = (String) _in, out = (String) _out;
    int i = in.indexOf("bla"), j = out.indexOf("bla");
    if (i < 0 || j < 0) fail();
    inPattern = "^" + patternQuote(in.substring(0, i))
      + "(.+)" + patternQuote(in.substring(i+3)) + "$";
    outPattern = Matcher.quoteReplacement(out.substring(0, j))
      + "$1" + Matcher.quoteReplacement(out.substring(j+3));
  }
  
  public Object processIn(Object _in) {
    String in = (String) _in;
    return in.replaceAll(inPattern, outPattern);
  }
}

Began life as a copy of #1000468