Iterating over integer[] in PL/pgSQL

I am trying to loop through an integer array (integer[]) in a plpgsql function. Something like this:

declare
    a integer[] = array[1,2,3];
    i bigint;
begin
    for i in a
loop 
    raise notice "% ",i;
end loop;
return true;
end

In my actual use case the integer array a is passed as parameter to the function. I get this error:

> ERROR: syntax error at or near "$1" > LINE 1: $1

How to loop through the array properly?

DO
$do$
DECLARE
   a integer[] := array[1,2,3];
   i integer;                      -- int, not bigint
BEGIN
   FOR i IN 1 .. array_upper(a, 1)
   LOOP
      RAISE NOTICE '%', a[i];      -- single quotes
   END LOOP;
END
$do$;

Or simpler with FOREACH in PostgreSQL 9.1 or later:

   FOREACH i IN ARRAY a
   LOOP 
      RAISE NOTICE '%', i;
   END LOOP;

For multi-dimensional arrays see:

• https://stackoverflow.com/questions/9783422/loop-over-array-dimension-in-plpgsql/9784986#9784986

However, set-based solutions with generate_series() or unnest() are often faster than looping over big sets. Basic examples:

• https://stackoverflow.com/questions/12327046/postgresql-frequency-table-expansion/12327440#12327440
• https://stackoverflow.com/questions/10747695/select-each-month-between-a-start-and-end-date/10747820#10747820

Search the tags [tag:generate-series] or [tag:unnest] for more.