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yap-6.3/CHR/chr/examples/scheduling.pl
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Prolog

% 980312 Thom Fruehwirth, LMU
:- use_module(library(chr)).
handler scheduling.
option(check_guard_bindings, on).
constraints leq/2, optimize/0.
% leq(X+N,Y) means: task X starts at least N time units before task Y
% assumes leq-relation is non-circular
redundant @ leq(N,Y), leq(M,Y) <=> M=<N | leq(N,Y).
% optimize gives smallest possible value to a variable
optimize @ optimize#Id \ leq(X,Y) <=>
ground(X),var(Y),findall_constraints(Y,leq(_,Y),L),L=[]
|
Y is X
pragma passive(Id).
% classical example --------------------------------------
build_house([Start,A,B,C,D,E,F,G,H,I,J,End]) :-
leq(Start+0,A),
leq(A+7,B),
leq(A+7,D),
leq(B+3,C),
leq(C+1,E),
leq(D+8,E),
leq(C+1,G),
leq(D+8,G),
leq(D+8,F),
leq(C+1,F),
leq(F+1,H),
leq(H+3,I),
leq(G+1,J),
leq(E+2,J),
leq(I+2,J),
leq(J+1,End),
optimize,
Start=0.
/*
| ?- build_house([Start,A,B,C,D,E,F,G,H,I,J,End]).
A = 0,
B = 7,
C = 10,
D = 7,
E = 15,
F = 15,
G = 15,
H = 16,
I = 19,
J = 21,
End = 22,
Start = 0,
optimize ?
*/
% end of handler scheduling