sql query with join and parameter in postgresql function

Hello,

I'd like to write a function similar to that:

------------------------------------------------
CREATE FUNCTION public.report_join_parameter(char(6)) RETURNS ??? AS
'
SELECT

tableA.field1,
tableA.field2,
tableB.field1,
tableB.field2,
tableC.field1,
tableC.field2,

FROM tableA

INNER JOIN tableB
ON tableA.pk = tableB.fk

INNER JOIN tableC
ON tableB.pk = tableC.fk

WHERE tableC.field3= 0
AND tableB.field1= $1
' LANGUAGE 'sql' VOLATILE;
------------------------------------------------

Do I ***HAVE TO*** define a composite type for the columns my function
is supposed to return? Isn't there a simpler method, that could allow me
to avoid this extra work?

I thought a view would be more appropriate, but if I'm not wrong, a view
does not accept any parameter as input...

Thanks!

Philippe