/usr/share/Yap/chr/a_star.pl is in yap 5.1.3-6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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% Author: Tom Schrijvers
% Email: Tom.Schrijvers@cs.kuleuven.be
% Copyright: K.U.Leuven 2004
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
:- module(a_star,
[
a_star/4
]).
:- use_module(binomialheap).
:- use_module(find).
:- use_module(hprolog).
a_star(DataIn,FinalData,ExpandData,DataOut) :-
a_star_node(DataIn,0,InitialNode),
empty_q(NewQueue),
insert_q(NewQueue,InitialNode,Queue),
a_star_aux(Queue,FinalData,ExpandData,EndNode),
a_star_node(DataOut,_,EndNode).
a_star_aux(Queue,FinalData,ExpandData,EndNode) :-
delete_min_q(Queue,Queue1,Node),
( final_node(FinalData,Node) ->
Node = EndNode
;
expand_node(ExpandData,Node,Nodes),
insert_list_q(Nodes,Queue1,NQueue),
a_star_aux(NQueue,FinalData,ExpandData,EndNode)
).
final_node(D^Call,Node) :-
a_star_node(Data,_,Node),
term_variables(Call,Vars),
chr_delete(Vars,D,DVars),
copy_term(D^Call-DVars,Data^NCall-DVars),
call(NCall).
expand_node(D^Ds^C^Call,Node,Nodes) :-
a_star_node(Data,Score,Node),
term_variables(Call,Vars),
chr_delete(Vars,D,DVars0),
chr_delete(DVars0,Ds,DVars1),
chr_delete(DVars1,C,DVars),
copy_term(D^Ds^C^Call-DVars,Data^EData^Cost^NCall-DVars),
term_variables(Node,NVars,DVars),
find_with_var_identity(ENode,NVars,(NCall,EScore is Cost + Score,a_star:a_star_node(EData,EScore,ENode)),Nodes).
a_star_node(Data,Score,Data-Score).
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