What is PDL::PP?
Simple answer: PDL::PP is both a glue between external libraries and PDL and a concise language for writing PDL functions. Slightly longer answer: PDL::PP is used to compile very concise definitions into XSUB routines implemented in C that can easily be called from PDL and which automatically support threading, dataflow and other things without you having to worry about it. For further details check PDL::PP and the section on “Extensions of PDL”.