How to return a modified array from a user-define function...

Hi:

I would like to create a standard deviation function using the basic
SQL statements "CREATE AGGREGATE" and "CREATE FUNCTION" using Postgres 7.0.2.

I can't find a way to return a modified array.

I've tried things like:

CREATE function x (_float8, float8) RETURNS _float8 AS
'SELECT {$1[1] + 1, $1[2] + $2, $1[3] + ($2 * $2)};'
LANGUAGE 'sql';

This doesn't work. I get the following error:

ERROR:  parser: parse error at or near "{"

Any help will be appreciated!
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