Prologの技芸 9.2節の練習問題

(1)

% occurrences(Sub,Term,N) :-
%  項Term中の部分項Subの出現回数がNのとき真になる．

occurrences(Term,Term,1) :- !.
occurrences(Sub,Term,N) :-
 compound(Term), !,
 functor(Term,F,M), occurrences(M,Sub,Term,0,N).
occurrences(Sub,Term,0).
occurrences(M,Sub,Term,N1,N2) :-
 M > 0, !, arg(M,Term,Arg), occurrences(Sub,Arg,N),
 N3 is N+N1, M1 is M-1, occurrences(M1,Sub,Term,N3,N2).
occurrences(0,Sub,Term,N,N).

(2)

% position(Subterm,Term,Position) :-
%  Positionは項Term中の部分項Subtermが占める
%  引数位置のリストである．

position(Term,Term,[]) :- !.
position(Sub,Term,Path) :-
 compound(Term), functor(Term,F,N),
 position(N,Sub,Term,Path), !.
position(N,Sub,Term,[N|Path]) :-
 arg(N,Term,Arg), position(Sub,Arg,Path).
position(N,Sub,Term,Path) :-
 N > 1, N1 is N-1, position(N1,Sub,Term,Path).

(3)

% univ(Term,List) :-
%  Listは，Termの関数子と，その後ろに
%  Termの引数を連ねたものからなるリストである．

univ(Term,[F|Args]) :-
 functor(Term,F,N), args(N,Term,Args,[]).
args(N,Term,Xs,Ys) :-
 N > 0, N1 is N-1,
 arg(N,Term,Arg), args(N1,Term,Xs,[Arg|Ys]).
args(0,Term,Xs,Xs).

(4)

% functor1(Term,F,Arity) :-
%  Termは，主関数子の名前がFで
%  引数の数がArityであるような項である．

functor1(Term,F,N) :-
 Term =.. [F|Args], length(Args,N).

% arg1(N,Term,Arg) :-
%  Argは，項TermのN番目の引数である．
arg1(N,Term,Arg) :-
 Term =.. [F|Args], retrieve(N,Args,Arg).

retrieve(1,[X|Xs],X).
retrieve(N,[X|Xs],Y) :-
 N > 1, N1 is N-1, retrieve(N1,Xs,Y).

(5)

% substitute(Old,New,OldTerm,NewTerm) :-
%  NewTermは，OldTerm中のOldをNewに置き換えたものである．

substitute(Old,New,Old,New).
substitute(Old,New,Term,Term) :-
 atomic(Term), Term \= Old.
substitute(Old,New,Term,Term1) :-
 compound(Term),
 Term =.. [F|Args],
 substitute_args(Old,New,Args,Args1),
 Term1 =.. [F|Args1].
substitute_args(Old,New,[Arg|Args],[Arg1|Args1]) :-
 substitute(Old,New,Arg,Arg1),
 substitute_args(Old,New,Args,Args1).
substitute_args(Old,New,[],[]).