53 lines
1.1 KiB
Prolog
53 lines
1.1 KiB
Prolog
% PATH CONSISTENCY, simple
|
|
% thom fruehwirth ECRC 941201, simplified version of time-pc.chr
|
|
% 980311 Thom Fruehwirth, LMU, adapted to Sicstus CHR
|
|
|
|
:- use_module(library(chr)).
|
|
|
|
handler path.
|
|
|
|
option(already_in_heads,on).
|
|
|
|
constraints con/3.
|
|
% con(X,Y,C) means that constraint C holds between variables X and Y
|
|
|
|
intersect_xy_xy @ con(X, Y, C1), con(X, Y, C2) <=>
|
|
inter(C1, C2, C3),
|
|
con(X,Y,C3).
|
|
intersect_xy_yx @ con(X, Y, C1), con(Y, X, CR) <=>
|
|
invert(CR, C2),
|
|
inter(C1, C2, C3),
|
|
con(X,Y,C3).
|
|
|
|
propagate_xy_yz @ con(X, Y, C1), con(Y, Z, C2) ==>
|
|
trans(C1, C2, C3)
|
|
|
|
|
con(X, Z, C3).
|
|
propagate_xy_xz @ con(X, Y, CR), con(X, Z, C2) ==>
|
|
invert(CR,C1),
|
|
trans(C1, C2, C3)
|
|
|
|
|
con(Y, Z, C3).
|
|
propagate_xy_zy @ con(X, Y, C1), con(Z, Y, CR) ==>
|
|
invert(CR,C2),
|
|
trans(C1, C2, C3)
|
|
|
|
|
con(X, Z, C3).
|
|
|
|
|
|
% Example ---------------------------------
|
|
% constraints are < and >
|
|
|
|
invert(<,>).
|
|
invert(>,<).
|
|
|
|
% fail if empty constraint would be produced
|
|
inter(C,C,C).
|
|
|
|
% fail if most general constraint would be produced
|
|
trans(C,C,C).
|
|
|
|
% ?- con(A,B,>),con(A,C,>),con(B,D,>),con(C,D,>).
|
|
|
|
/*--------------- eof path.pl ----------------------------------------------*/
|