%
% Bill of Material problem
%
% psb(P1, P2, QT) denotes that P1 contains P2 in quantiy QT.
% basic(P, Price) denotes elmentary parts purchasable for a
% price.

%%
database( {
	psb(P1:string, P2:string, QT:integer),	
	basic(P:string, C:integer),
	prolfc(P:string, C:integer)
} ).
    
%%
export part_cost(P,S,C).
export prolfc($P,C).

%%
part_cost(Part, 0, Cost)<-basic(Part,Cost). 
part_cost(Part, mcount<Sb>, msum<MCost>)<-
    part_cost(Sb, ChC, Cst), prolfc(Sb, ChC), 
    psb(Part, Sb, Mult), MCost = Cst * Mult.

%prolfc(P1,0)<-basic(P1,_).
%prolfc(P1,count<P2>)<-psb(P1,P2,_).

single(mcount, X, 1).
multi(mcount,  X, Old, New) <- New=Old+1.
return(mcount, X, Old, New) <- if (Old =nil then New=1 else New=Old+1).

single(msum, X, X).
multi(msum,  X, Old, S) <- S=X+Old.
return(msum, X, Old, S) <- if (Old=nil then S=X else S=X+Old).