How to CREATE FUNCTION into PostgreSQL

Hi,

I need to create a function to convert a string with a portuguese float-point
representation ( thousand sep = dot, decimal point = comma) to a float8.

When I execute the SQL:
SELECT replace(replace ('1.234.567,08', '.', ''), ',' , '.')::float8 AS test;

the result was the number 1234567.08, which may insert
as a float8 field of a table

When I issue the SQL:
CREATE FUNCTION to_double(text) RETURNS float8 AS
'SELECT (replace(replace(text, '.' , '') , ',' , '.')::float8 AS RESULT
LANGUAGE SQL

it generates an error and function isn't created.

Someone can help me?

Thaks in advance,
Marcos