pgSQL, executing generic query - Mailing list pgsql-sql

Hi,
I should to write a function which has one text parameter ;
throught this parameter a query will be passed to the function;
in the function the query will be executed and the result put in the 
record type;
the problem is:
how can I to get the columns value if the query is not defined a priori?
i.e. I can't use the contruct "record".fieldname

I've searched everywhere but nothing.
is it possible with pgSQL? have you any suggest?

Thanks,
Alessandro