%
% Ex.1 return averages every 5 records
%
% Haixun Wang, hxwang@cs.ucla.edu

%%
database( {
	q(P:integer, X:integer)
} ).

%%
export p(P,A).

%%
p(P, myavg<A>)<-q(P,A).

single(myavg, X, (X,1)).
multi(myavg,  Xs, (Xo,Co), (X,C)) <- X=Xs+Xo, C=1+Co.
return(myavg, X, (Yo,Co), A) <- if (X=nil 
				then A= Yo * 1.0 / Co
				else mod(Co,5), A = Yo * 1.0 / Co).
mod(X,X).
mod(X,Y)<- X>Y, mod(X-Y,Y).