Questions about anonymous procedure/function.

Greetings,

I have a question about whether I am able to create an *anonymous*
procedure/function under postgreSQL 8. Something like:

Begin
... ...
update ...
IF ... THEN
rollback
END IF;
... ...
END;

I'd like to do a series of operations. If any one of the opers failed,
all previous operation will rollback. Actually, I do not want to create
named functions. Just used the structure for different tables with minor
changes.

Another question is about how to create a function/procedure do not need
a return value (void for return value). It seems that postgreSQL forces
to return some value?

Thanks a lot!
Emi