%% Return Rules in User-Defined Aggregates

% Schema
%-------
database({sppp(S:string, Item:string, Price:integer),
	  stock_closing(Company:string, Price:real)}).

%Derivated predicates and rules
%------------------------------
% General format
%	return(newaggr, NewY, OldV, VR) <- ...
%
% Find suppliers who supply more than 7 items
select(Sup) <- allcounts(Sup, CC), CC > 7 .  
allcounts(Sup, cntol<Itm>) <- sppp(Sup, Itm, Price).

single(cntol, _, 1).
multi(cntol, S, Old, New) <- New = Old+1. 
ereturn(cntol, S, Old, Value) <- Old ~= nil, Value = Old+1.

export select(X).

% Moving time window aggregation :
% Average the prices of IBM stocks over the last five days.
result(mw5avg<Stock>) <- stock_closing('IBM', Stock).

single(mw5avg, X, [X]).
multi(mw5avg, X, OL, NL) <- if(OL= [X1, X2, X3, X4, X5]
				then  L = [X1, X2, X3, X4] 
				else  L = OL),
			    NL = [X | L].
ereturn(mw5avg, _, [X5,X4,X3,X2,X1], Avg) <- Avg = (X1+X2+X3+X4+X5)/5.

export result(X).