Debug Info from Moodle Plugin

I am a newbie to Moodle. I am trying to create a local plug which would do tasks (sending email) automatically when user is enrolled / unenrolled. While developing this plugin, I am trying to `echo` or `print_r` some information for debug and tracing purposes. The code is as simple as function perform_enrol($eventdata){ echo 'Hello World'; print_r($eventdata); return true; } However, when the code executes, I get the following error occurs: > Syntax Error File: > http://192.168.10.60/moodle/theme/yui_combo.php?3.9.1/build/simpleyui/simpleyui.js&3.9.1/build/loader/loader.js > Line: 18541 When I comment out the `echo` and `print_r` , the code works fine. The same problem continues for `print_object` , `debug` or any other printing functions. Is there a specific way to print from plugins. I have used these functions in core code in past and seems to work fine.