How to debug a plpgsql script.

I've got several problems with my own little plpgsql script. How could I
debug it? I mean something like in 'C' when someone fills the code with
"printf"'s.

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Sebestyén Zoltán <szoli@netvisor.hu>    I'm believing that the Holy Spirit is
                    gonna allow the hand, and the foot, and
MAKE INSTALL NOT WAR            the mouth, just to begin to speak, and
                                        to minister, and to heal coordinated by
                    the head.

I use UNIX because reboots are for hardware upgrades.

              -- Waiting for FreeBSD 2.2.8, not Godot! --