[exim] calling mysql stored procedures from Exim

I am trying to call a mysql stored procedure which returns a results set
to Exim:

${lookup mysql{servers=host/foo/user/password; call
bar('stuff')}{$value}{not found}}

but I'm getting the error:

gave DEFER: MYSQL: query failed: PROCEDURE foo.bar can't return a result
set in the given context

the procedure looks like (yes, the names have been changed to protect the
inicent, but it really is a one line sp):

create procedure bar(p varchar(32))
begin
select col1,col2,col3 from tab1 where col4=p;
end

From the command line, the mysql client runs this sp just fine and returns

results.

Any ideas from anyone??

Thanks,

Dan