docs: private synchronized void returnPressed() {
          Document doc = getDocument();
          int len = doc.getLength();
          Segment segment = new Segment();
          try {
              doc.getText(outputMark, len - outputMark, segment);
          } catch (javax.swing.text.BadLocationException ignored) {
              ignored.printStackTrace();
          }
          String text = segment.toString();
          if (debugGui.dim.stringIsCompilableUnit(text)) {
              if (text.trim().length() > 0) {
                 history.add(text);
                 historyIndex = history.size();
              }
              append("\n");
              String result = debugGui.dim.eval(text);
              if (result.length() > 0) {
                  append(result);
                  append("\n");
              }
              append("% ");
              outputMark = doc.getLength();
          } else {
              append("\n");
          }
      }