Firebird: Gostaria que essa função, na clausula where, o l.destino recebesse a variavel @destino, porém preciso concatenar ela a uma string.

CREATE FUNCTION [dbo].[MinhaFuncao](@destino VARCHAR(max))
RETURNS TABLE
AS
RETURN (
SELECT *
FROM OpenQuery(TOTALIP,
'SELECT
c.nome AS NOME,
CASE
WHEN u.nome IS NULL THEN ''''
ELSE u.nome
END AS OPERADOR,
l.data AS DATA,
CASE
WHEN l.status = ''ANSWERED'' THEN ''ATENDIDA''
WHEN l.status = ''NO ANSWER'' THEN ''NÃO ATENDIDA''
WHEN l.status = ''FAILED'' THEN ''FALHA''
ELSE l.status
END AS STATUS,
CASE
WHEN LENGTH(l.destino) = 12 AND LEFT(l.destino, 1) = ''0'' THEN LTRIM(l.destino, ''0'')
-- WHEN LENGTH(l.destino) = 9 THEN CONCAT(''11'', l.destino)
ELSE l.destino
END AS DESTINO,
CURRENT_DATE AS DISCAGEM
FROM
public.ligacoes_ativo l
INNER JOIN public.campanhas c ON l.id_campanha = c.id
LEFT JOIN public.usuarios u ON l.ramal = u.ramal
WHERE
l.data >= CURRENT_DATE
AND l.destino = ||'@destino'|| '));
GO