If you need to debug a variable or function in Prestashop (PHP, not Smarty) you can use this piece of code. Logging in Prestashop is not very well documented, so I had to dive into the code to figure out how to do it:
$logger = new FileLogger(0); //0 == debug level, logDebug() won’t work without this.
Debug messages will look like this (inside “/log/debug.log” at root dir in Prestashop):
*DEBUG* 2014/02/11 – 14:31:48: Hello world
I hope this helps somebody :-). Cheers.