%% Arithmetic in DeAL

% Schema
%-------
database({b(integer, integer)}).

%Derivated predicates and rules
%------------------------------
result(X) <- b(A, B), X = A/B.
export result(X).

% Schema
%-------
database({city(Name:string, State:string, Population:integer),
	  distance(City1:string, City2:string, Distance:float)
	 }).

%Derivated predicates and rules
%------------------------------
% User may try
%	query distance_feet('Austin', 'Bastrop', Z)
% system would return
%	distance_feet('Austin', 'Bastrop', 158400).
%	-- 1 solution

distance_feet1(X, Z, W) <- distance(X, Z, Y), W = 5280 * Y. 
distance_feet(X, Z, 5280 * Y) <- distance(X, Z, Y).

export distance_feet1($X, $Z,  Y).
export distance_feet($X, $Z,  Y).

% ``List all cities which are within 100 miles of Austin''. 
% User may try
%	query close( 'Austin', City, 100)
% System would return
%	close('Austin', 'San_antonio', 100).
%	close('Austin', 'Bastrop', 100).
%	-- 2 solutions
%
% The query form: export close($X, Y, Z) will not compile
% because it is not safe.
% Also
%	close1(X, Y, Z) <- W < Z, distance(X, Y, W).
%	export close1($X, Y, $Z).
% is not safe either.

close(X, Y, Z) <- distance(X, Y, W), W < Z.
export close($X, Y, $Z).