You might want to have a look at Chapter 10, Publishing Your Code as PostgreSQL. That chapter includes some samples (and an extremely handy way to install them) that will be useful here in this part of the book. The examples will be shown again here in the text of this chapter, but they would be quite a bit easier for you to install as an extension.
Here is the first promised example:
CREATE OR REPLACE FUNCTION format_us_full_name_debug(
prefix text,
firstname text,
mi text,
lastname text,
suffix text)
RETURNS text AS
$BODY$
DECLARE
fname_mi text;
fmi_lname text;
prefix_fmil text;
pfmil_suffix text;
BEGIN
fname_mi := CONCAT_WS(' ', CASE trim(firstname) WHEN '' THEN NULL ELSE firstname END, CASE trim(mi) WHEN '' THEN NULL ELSE mi END...