PL/SQL: function call like $1($2)

I want to create a function in PL/SQL as
CREATE OR REPLACE FUNCTION "f_do" (text, double precision[]) RETURNS
double precision AS '
DECLARE
f text := $1;
p double precision[] := $2;
res double precision;
BEGIN
SELECT f(p) into res;
RETURN res;
END;' LANGUAGE "plpgsql"
STABLE
RETURNS NULL ON NULL INPUT
SECURITY INVOKER

But it does not work.
I try EXECUTE f || ' ( ' || p || ' );' INTO res
But is does not work too.
There is no function to convert double precision[] to text.

Is it possible to do this without converting the array of double to
text ?

Pailloncy Jean-Gerard