Obtain boolean value of expression in PLPGSQL

Hello

My task is to validate expression and get value of it in boolean variable.
I try to do following:
CREATE OR REPLACE FUNCTION get_value(integer) RETURNS boolean AS'
DECLARE
Ret boolean;
Op TEXT = ''='';
BEGIN

Ret := 3 || Op || $1;
RETURN Ret;
END;
' language 'plpgsql';

when I try to execute this function I get such result:

bill=# select get_value(3);
WARNING: Error occurred while executing PL/pgSQL function get_value
WARNING: line 6 at assignment
ERROR: Bad boolean external representation '3=3'
bill=#

So, how can I explain that resulting type must be boolean ? Also, I try to
play with SELECT INTO with same result.

--
... All opinions expressed are mine and not those of my employer.

Yours, Max [Msg N 2419]
-------------------------------------------
mailto: mx(at)lucky(dot)net phone: +380-44-2054455