cast bytea to text

Dear List,

How can i cast bytea to text?
I´ve read about the DECODE function, but my 8.1 backend doesn´t recognize it.
I´m trying to create an implicit cast using the function:

create or replace function bytea2text(bytea) returns text as
$$
select DECODE($1, 'escape');
$$
language sql strict;

Answer:
ERROR: function decode(bytea, "unknown") does not exist
SQL state: 42883
Hint: No function matches the given name and argument types. You may need to add explicit type casts.
Context: SQL function "bytea2text"